YQ Connector: support managed ClickHouse

Со стороны dqrun можно обратиться к инстансу коннектора, который работает на streaming стенде, и извлечь данные из облачного CH.

1 files changed, 5251 insertions, 0 deletions

diff --git a/contrib/libs/llvm16/lib/Transforms/Scalar/SROA.cpp b/contrib/libs/llvm16/lib/Transforms/Scalar/SROA.cpp
new file mode 100644
index 0000000000..8339981e1b
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+++ b/contrib/libs/llvm16/lib/Transforms/Scalar/SROA.cpp
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+//===- SROA.cpp - Scalar Replacement Of Aggregates ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This transformation implements the well known scalar replacement of
+/// aggregates transformation. It tries to identify promotable elements of an
+/// aggregate alloca, and promote them to registers. It will also try to
+/// convert uses of an element (or set of elements) of an alloca into a vector
+/// or bitfield-style integer scalar if appropriate.
+///
+/// It works to do this with minimal slicing of the alloca so that regions
+/// which are merely transferred in and out of external memory remain unchanged
+/// and are not decomposed to scalar code.
+///
+/// Because this also performs alloca promotion, it can be thought of as also
+/// serving the purpose of SSA formation. The algorithm iterates on the
+/// function until all opportunities for promotion have been realized.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/SROA.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallBitVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/ADT/iterator.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/DomTreeUpdater.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/Analysis/PtrUseVisitor.h"
+#include "llvm/Config/llvm-config.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/ConstantFolder.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GetElementPtrTypeIterator.h"
+#include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/Use.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/PromoteMemToReg.h"
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <iterator>
+#include <string>
+#include <tuple>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+using namespace llvm::sroa;
+
+#define DEBUG_TYPE "sroa"
+
+STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement");
+STATISTIC(NumAllocaPartitions, "Number of alloca partitions formed");
+STATISTIC(MaxPartitionsPerAlloca, "Maximum number of partitions per alloca");
+STATISTIC(NumAllocaPartitionUses, "Number of alloca partition uses rewritten");
+STATISTIC(MaxUsesPerAllocaPartition, "Maximum number of uses of a partition");
+STATISTIC(NumNewAllocas, "Number of new, smaller allocas introduced");
+STATISTIC(NumPromoted, "Number of allocas promoted to SSA values");
+STATISTIC(NumLoadsSpeculated, "Number of loads speculated to allow promotion");
+STATISTIC(NumLoadsPredicated,
+          "Number of loads rewritten into predicated loads to allow promotion");
+STATISTIC(
+    NumStoresPredicated,
+    "Number of stores rewritten into predicated loads to allow promotion");
+STATISTIC(NumDeleted, "Number of instructions deleted");
+STATISTIC(NumVectorized, "Number of vectorized aggregates");
+
+/// Hidden option to experiment with completely strict handling of inbounds
+/// GEPs.
+static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds", cl::init(false),
+                                        cl::Hidden);
+namespace {
+/// Find linked dbg.assign and generate a new one with the correct
+/// FragmentInfo. Link Inst to the new dbg.assign.  If Value is nullptr the
+/// value component is copied from the old dbg.assign to the new.
+/// \param OldAlloca             Alloca for the variable before splitting.
+/// \param RelativeOffsetInBits  Offset into \p OldAlloca relative to the
+///                              offset prior to splitting (change in offset).
+/// \param SliceSizeInBits       New number of bits being written to.
+/// \param OldInst               Instruction that is being split.
+/// \param Inst                  New instruction performing this part of the
+///                              split store.
+/// \param Dest                  Store destination.
+/// \param Value                 Stored value.
+/// \param DL                    Datalayout.
+static void migrateDebugInfo(AllocaInst *OldAlloca,
+                             uint64_t RelativeOffsetInBits,
+                             uint64_t SliceSizeInBits, Instruction *OldInst,
+                             Instruction *Inst, Value *Dest, Value *Value,
+                             const DataLayout &DL) {
+  auto MarkerRange = at::getAssignmentMarkers(OldInst);
+  // Nothing to do if OldInst has no linked dbg.assign intrinsics.
+  if (MarkerRange.empty())
+    return;
+
+  LLVM_DEBUG(dbgs() << "  migrateDebugInfo\n");
+  LLVM_DEBUG(dbgs() << "    OldAlloca: " << *OldAlloca << "\n");
+  LLVM_DEBUG(dbgs() << "    RelativeOffset: " << RelativeOffsetInBits << "\n");
+  LLVM_DEBUG(dbgs() << "    SliceSizeInBits: " << SliceSizeInBits << "\n");
+  LLVM_DEBUG(dbgs() << "    OldInst: " << *OldInst << "\n");
+  LLVM_DEBUG(dbgs() << "    Inst: " << *Inst << "\n");
+  LLVM_DEBUG(dbgs() << "    Dest: " << *Dest << "\n");
+  if (Value)
+    LLVM_DEBUG(dbgs() << "    Value: " << *Value << "\n");
+
+  // The new inst needs a DIAssignID unique metadata tag (if OldInst has
+  // one). It shouldn't already have one: assert this assumption.
+  assert(!Inst->getMetadata(LLVMContext::MD_DIAssignID));
+  DIAssignID *NewID = nullptr;
+  auto &Ctx = Inst->getContext();
+  DIBuilder DIB(*OldInst->getModule(), /*AllowUnresolved*/ false);
+  uint64_t AllocaSizeInBits = *OldAlloca->getAllocationSizeInBits(DL);
+  assert(OldAlloca->isStaticAlloca());
+
+  for (DbgAssignIntrinsic *DbgAssign : MarkerRange) {
+    LLVM_DEBUG(dbgs() << "      existing dbg.assign is: " << *DbgAssign
+                      << "\n");
+    auto *Expr = DbgAssign->getExpression();
+
+    // Check if the dbg.assign already describes a fragment.
+    auto GetCurrentFragSize = [AllocaSizeInBits, DbgAssign,
+                               Expr]() -> uint64_t {
+      if (auto FI = Expr->getFragmentInfo())
+        return FI->SizeInBits;
+      if (auto VarSize = DbgAssign->getVariable()->getSizeInBits())
+        return *VarSize;
+      // The variable type has an unspecified size. This can happen in the
+      // case of DW_TAG_unspecified_type types, e.g.  std::nullptr_t. Because
+      // there is no fragment and we do not know the size of the variable type,
+      // we'll guess by looking at the alloca.
+      return AllocaSizeInBits;
+    };
+    uint64_t CurrentFragSize = GetCurrentFragSize();
+    bool MakeNewFragment = CurrentFragSize != SliceSizeInBits;
+    assert(MakeNewFragment || RelativeOffsetInBits == 0);
+
+    assert(SliceSizeInBits <= AllocaSizeInBits);
+    if (MakeNewFragment) {
+      assert(RelativeOffsetInBits + SliceSizeInBits <= CurrentFragSize);
+      auto E = DIExpression::createFragmentExpression(
+          Expr, RelativeOffsetInBits, SliceSizeInBits);
+      assert(E && "Failed to create fragment expr!");
+      Expr = *E;
+    }
+
+    // If we haven't created a DIAssignID ID do that now and attach it to Inst.
+    if (!NewID) {
+      NewID = DIAssignID::getDistinct(Ctx);
+      Inst->setMetadata(LLVMContext::MD_DIAssignID, NewID);
+    }
+
+    Value = Value ? Value : DbgAssign->getValue();
+    auto *NewAssign = DIB.insertDbgAssign(
+        Inst, Value, DbgAssign->getVariable(), Expr, Dest,
+        DIExpression::get(Ctx, std::nullopt), DbgAssign->getDebugLoc());
+
+    // We could use more precision here at the cost of some additional (code)
+    // complexity - if the original dbg.assign was adjacent to its store, we
+    // could position this new dbg.assign adjacent to its store rather than the
+    // old dbg.assgn. That would result in interleaved dbg.assigns rather than
+    // what we get now:
+    //    split store !1
+    //    split store !2
+    //    dbg.assign !1
+    //    dbg.assign !2
+    // This (current behaviour) results results in debug assignments being
+    // noted as slightly offset (in code) from the store. In practice this
+    // should have little effect on the debugging experience due to the fact
+    // that all the split stores should get the same line number.
+    NewAssign->moveBefore(DbgAssign);
+
+    NewAssign->setDebugLoc(DbgAssign->getDebugLoc());
+    LLVM_DEBUG(dbgs() << "Created new assign intrinsic: " << *NewAssign
+                      << "\n");
+  }
+}
+
+/// A custom IRBuilder inserter which prefixes all names, but only in
+/// Assert builds.
+class IRBuilderPrefixedInserter final : public IRBuilderDefaultInserter {
+  std::string Prefix;
+
+  Twine getNameWithPrefix(const Twine &Name) const {
+    return Name.isTriviallyEmpty() ? Name : Prefix + Name;
+  }
+
+public:
+  void SetNamePrefix(const Twine &P) { Prefix = P.str(); }
+
+  void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB,
+                    BasicBlock::iterator InsertPt) const override {
+    IRBuilderDefaultInserter::InsertHelper(I, getNameWithPrefix(Name), BB,
+                                           InsertPt);
+  }
+};
+
+/// Provide a type for IRBuilder that drops names in release builds.
+using IRBuilderTy = IRBuilder<ConstantFolder, IRBuilderPrefixedInserter>;
+
+/// A used slice of an alloca.
+///
+/// This structure represents a slice of an alloca used by some instruction. It
+/// stores both the begin and end offsets of this use, a pointer to the use
+/// itself, and a flag indicating whether we can classify the use as splittable
+/// or not when forming partitions of the alloca.
+class Slice {
+  /// The beginning offset of the range.
+  uint64_t BeginOffset = 0;
+
+  /// The ending offset, not included in the range.
+  uint64_t EndOffset = 0;
+
+  /// Storage for both the use of this slice and whether it can be
+  /// split.
+  PointerIntPair<Use *, 1, bool> UseAndIsSplittable;
+
+public:
+  Slice() = default;
+
+  Slice(uint64_t BeginOffset, uint64_t EndOffset, Use *U, bool IsSplittable)
+      : BeginOffset(BeginOffset), EndOffset(EndOffset),
+        UseAndIsSplittable(U, IsSplittable) {}
+
+  uint64_t beginOffset() const { return BeginOffset; }
+  uint64_t endOffset() const { return EndOffset; }
+
+  bool isSplittable() const { return UseAndIsSplittable.getInt(); }
+  void makeUnsplittable() { UseAndIsSplittable.setInt(false); }
+
+  Use *getUse() const { return UseAndIsSplittable.getPointer(); }
+
+  bool isDead() const { return getUse() == nullptr; }
+  void kill() { UseAndIsSplittable.setPointer(nullptr); }
+
+  /// Support for ordering ranges.
+  ///
+  /// This provides an ordering over ranges such that start offsets are
+  /// always increasing, and within equal start offsets, the end offsets are
+  /// decreasing. Thus the spanning range comes first in a cluster with the
+  /// same start position.
+  bool operator<(const Slice &RHS) const {
+    if (beginOffset() < RHS.beginOffset())
+      return true;
+    if (beginOffset() > RHS.beginOffset())
+      return false;
+    if (isSplittable() != RHS.isSplittable())
+      return !isSplittable();
+    if (endOffset() > RHS.endOffset())
+      return true;
+    return false;
+  }
+
+  /// Support comparison with a single offset to allow binary searches.
+  friend LLVM_ATTRIBUTE_UNUSED bool operator<(const Slice &LHS,
+                                              uint64_t RHSOffset) {
+    return LHS.beginOffset() < RHSOffset;
+  }
+  friend LLVM_ATTRIBUTE_UNUSED bool operator<(uint64_t LHSOffset,
+                                              const Slice &RHS) {
+    return LHSOffset < RHS.beginOffset();
+  }
+
+  bool operator==(const Slice &RHS) const {
+    return isSplittable() == RHS.isSplittable() &&
+           beginOffset() == RHS.beginOffset() && endOffset() == RHS.endOffset();
+  }
+  bool operator!=(const Slice &RHS) const { return !operator==(RHS); }
+};
+
+} // end anonymous namespace
+
+/// Representation of the alloca slices.
+///
+/// This class represents the slices of an alloca which are formed by its
+/// various uses. If a pointer escapes, we can't fully build a representation
+/// for the slices used and we reflect that in this structure. The uses are
+/// stored, sorted by increasing beginning offset and with unsplittable slices
+/// starting at a particular offset before splittable slices.
+class llvm::sroa::AllocaSlices {
+public:
+  /// Construct the slices of a particular alloca.
+  AllocaSlices(const DataLayout &DL, AllocaInst &AI);
+
+  /// Test whether a pointer to the allocation escapes our analysis.
+  ///
+  /// If this is true, the slices are never fully built and should be
+  /// ignored.
+  bool isEscaped() const { return PointerEscapingInstr; }
+
+  /// Support for iterating over the slices.
+  /// @{
+  using iterator = SmallVectorImpl<Slice>::iterator;
+  using range = iterator_range<iterator>;
+
+  iterator begin() { return Slices.begin(); }
+  iterator end() { return Slices.end(); }
+
+  using const_iterator = SmallVectorImpl<Slice>::const_iterator;
+  using const_range = iterator_range<const_iterator>;
+
+  const_iterator begin() const { return Slices.begin(); }
+  const_iterator end() const { return Slices.end(); }
+  /// @}
+
+  /// Erase a range of slices.
+  void erase(iterator Start, iterator Stop) { Slices.erase(Start, Stop); }
+
+  /// Insert new slices for this alloca.
+  ///
+  /// This moves the slices into the alloca's slices collection, and re-sorts
+  /// everything so that the usual ordering properties of the alloca's slices
+  /// hold.
+  void insert(ArrayRef<Slice> NewSlices) {
+    int OldSize = Slices.size();
+    Slices.append(NewSlices.begin(), NewSlices.end());
+    auto SliceI = Slices.begin() + OldSize;
+    llvm::sort(SliceI, Slices.end());
+    std::inplace_merge(Slices.begin(), SliceI, Slices.end());
+  }
+
+  // Forward declare the iterator and range accessor for walking the
+  // partitions.
+  class partition_iterator;
+  iterator_range<partition_iterator> partitions();
+
+  /// Access the dead users for this alloca.
+  ArrayRef<Instruction *> getDeadUsers() const { return DeadUsers; }
+
+  /// Access Uses that should be dropped if the alloca is promotable.
+  ArrayRef<Use *> getDeadUsesIfPromotable() const {
+    return DeadUseIfPromotable;
+  }
+
+  /// Access the dead operands referring to this alloca.
+  ///
+  /// These are operands which have cannot actually be used to refer to the
+  /// alloca as they are outside its range and the user doesn't correct for
+  /// that. These mostly consist of PHI node inputs and the like which we just
+  /// need to replace with undef.
+  ArrayRef<Use *> getDeadOperands() const { return DeadOperands; }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  void print(raw_ostream &OS, const_iterator I, StringRef Indent = "  ") const;
+  void printSlice(raw_ostream &OS, const_iterator I,
+                  StringRef Indent = "  ") const;
+  void printUse(raw_ostream &OS, const_iterator I,
+                StringRef Indent = "  ") const;
+  void print(raw_ostream &OS) const;
+  void dump(const_iterator I) const;
+  void dump() const;
+#endif
+
+private:
+  template <typename DerivedT, typename RetT = void> class BuilderBase;
+  class SliceBuilder;
+
+  friend class AllocaSlices::SliceBuilder;
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  /// Handle to alloca instruction to simplify method interfaces.
+  AllocaInst &AI;
+#endif
+
+  /// The instruction responsible for this alloca not having a known set
+  /// of slices.
+  ///
+  /// When an instruction (potentially) escapes the pointer to the alloca, we
+  /// store a pointer to that here and abort trying to form slices of the
+  /// alloca. This will be null if the alloca slices are analyzed successfully.
+  Instruction *PointerEscapingInstr;
+
+  /// The slices of the alloca.
+  ///
+  /// We store a vector of the slices formed by uses of the alloca here. This
+  /// vector is sorted by increasing begin offset, and then the unsplittable
+  /// slices before the splittable ones. See the Slice inner class for more
+  /// details.
+  SmallVector<Slice, 8> Slices;
+
+  /// Instructions which will become dead if we rewrite the alloca.
+  ///
+  /// Note that these are not separated by slice. This is because we expect an
+  /// alloca to be completely rewritten or not rewritten at all. If rewritten,
+  /// all these instructions can simply be removed and replaced with poison as
+  /// they come from outside of the allocated space.
+  SmallVector<Instruction *, 8> DeadUsers;
+
+  /// Uses which will become dead if can promote the alloca.
+  SmallVector<Use *, 8> DeadUseIfPromotable;
+
+  /// Operands which will become dead if we rewrite the alloca.
+  ///
+  /// These are operands that in their particular use can be replaced with
+  /// poison when we rewrite the alloca. These show up in out-of-bounds inputs
+  /// to PHI nodes and the like. They aren't entirely dead (there might be
+  /// a GEP back into the bounds using it elsewhere) and nor is the PHI, but we
+  /// want to swap this particular input for poison to simplify the use lists of
+  /// the alloca.
+  SmallVector<Use *, 8> DeadOperands;
+};
+
+/// A partition of the slices.
+///
+/// An ephemeral representation for a range of slices which can be viewed as
+/// a partition of the alloca. This range represents a span of the alloca's
+/// memory which cannot be split, and provides access to all of the slices
+/// overlapping some part of the partition.
+///
+/// Objects of this type are produced by traversing the alloca's slices, but
+/// are only ephemeral and not persistent.
+class llvm::sroa::Partition {
+private:
+  friend class AllocaSlices;
+  friend class AllocaSlices::partition_iterator;
+
+  using iterator = AllocaSlices::iterator;
+
+  /// The beginning and ending offsets of the alloca for this
+  /// partition.
+  uint64_t BeginOffset = 0, EndOffset = 0;
+
+  /// The start and end iterators of this partition.
+  iterator SI, SJ;
+
+  /// A collection of split slice tails overlapping the partition.
+  SmallVector<Slice *, 4> SplitTails;
+
+  /// Raw constructor builds an empty partition starting and ending at
+  /// the given iterator.
+  Partition(iterator SI) : SI(SI), SJ(SI) {}
+
+public:
+  /// The start offset of this partition.
+  ///
+  /// All of the contained slices start at or after this offset.
+  uint64_t beginOffset() const { return BeginOffset; }
+
+  /// The end offset of this partition.
+  ///
+  /// All of the contained slices end at or before this offset.
+  uint64_t endOffset() const { return EndOffset; }
+
+  /// The size of the partition.
+  ///
+  /// Note that this can never be zero.
+  uint64_t size() const {
+    assert(BeginOffset < EndOffset && "Partitions must span some bytes!");
+    return EndOffset - BeginOffset;
+  }
+
+  /// Test whether this partition contains no slices, and merely spans
+  /// a region occupied by split slices.
+  bool empty() const { return SI == SJ; }
+
+  /// \name Iterate slices that start within the partition.
+  /// These may be splittable or unsplittable. They have a begin offset >= the
+  /// partition begin offset.
+  /// @{
+  // FIXME: We should probably define a "concat_iterator" helper and use that
+  // to stitch together pointee_iterators over the split tails and the
+  // contiguous iterators of the partition. That would give a much nicer
+  // interface here. We could then additionally expose filtered iterators for
+  // split, unsplit, and unsplittable splices based on the usage patterns.
+  iterator begin() const { return SI; }
+  iterator end() const { return SJ; }
+  /// @}
+
+  /// Get the sequence of split slice tails.
+  ///
+  /// These tails are of slices which start before this partition but are
+  /// split and overlap into the partition. We accumulate these while forming
+  /// partitions.
+  ArrayRef<Slice *> splitSliceTails() const { return SplitTails; }
+};
+
+/// An iterator over partitions of the alloca's slices.
+///
+/// This iterator implements the core algorithm for partitioning the alloca's
+/// slices. It is a forward iterator as we don't support backtracking for
+/// efficiency reasons, and re-use a single storage area to maintain the
+/// current set of split slices.
+///
+/// It is templated on the slice iterator type to use so that it can operate
+/// with either const or non-const slice iterators.
+class AllocaSlices::partition_iterator
+    : public iterator_facade_base<partition_iterator, std::forward_iterator_tag,
+                                  Partition> {
+  friend class AllocaSlices;
+
+  /// Most of the state for walking the partitions is held in a class
+  /// with a nice interface for examining them.
+  Partition P;
+
+  /// We need to keep the end of the slices to know when to stop.
+  AllocaSlices::iterator SE;
+
+  /// We also need to keep track of the maximum split end offset seen.
+  /// FIXME: Do we really?
+  uint64_t MaxSplitSliceEndOffset = 0;
+
+  /// Sets the partition to be empty at given iterator, and sets the
+  /// end iterator.
+  partition_iterator(AllocaSlices::iterator SI, AllocaSlices::iterator SE)
+      : P(SI), SE(SE) {
+    // If not already at the end, advance our state to form the initial
+    // partition.
+    if (SI != SE)
+      advance();
+  }
+
+  /// Advance the iterator to the next partition.
+  ///
+  /// Requires that the iterator not be at the end of the slices.
+  void advance() {
+    assert((P.SI != SE || !P.SplitTails.empty()) &&
+           "Cannot advance past the end of the slices!");
+
+    // Clear out any split uses which have ended.
+    if (!P.SplitTails.empty()) {
+      if (P.EndOffset >= MaxSplitSliceEndOffset) {
+        // If we've finished all splits, this is easy.
+        P.SplitTails.clear();
+        MaxSplitSliceEndOffset = 0;
+      } else {
+        // Remove the uses which have ended in the prior partition. This
+        // cannot change the max split slice end because we just checked that
+        // the prior partition ended prior to that max.
+        llvm::erase_if(P.SplitTails,
+                       [&](Slice *S) { return S->endOffset() <= P.EndOffset; });
+        assert(llvm::any_of(P.SplitTails,
+                            [&](Slice *S) {
+                              return S->endOffset() == MaxSplitSliceEndOffset;
+                            }) &&
+               "Could not find the current max split slice offset!");
+        assert(llvm::all_of(P.SplitTails,
+                            [&](Slice *S) {
+                              return S->endOffset() <= MaxSplitSliceEndOffset;
+                            }) &&
+               "Max split slice end offset is not actually the max!");
+      }
+    }
+
+    // If P.SI is already at the end, then we've cleared the split tail and
+    // now have an end iterator.
+    if (P.SI == SE) {
+      assert(P.SplitTails.empty() && "Failed to clear the split slices!");
+      return;
+    }
+
+    // If we had a non-empty partition previously, set up the state for
+    // subsequent partitions.
+    if (P.SI != P.SJ) {
+      // Accumulate all the splittable slices which started in the old
+      // partition into the split list.
+      for (Slice &S : P)
+        if (S.isSplittable() && S.endOffset() > P.EndOffset) {
+          P.SplitTails.push_back(&S);
+          MaxSplitSliceEndOffset =
+              std::max(S.endOffset(), MaxSplitSliceEndOffset);
+        }
+
+      // Start from the end of the previous partition.
+      P.SI = P.SJ;
+
+      // If P.SI is now at the end, we at most have a tail of split slices.
+      if (P.SI == SE) {
+        P.BeginOffset = P.EndOffset;
+        P.EndOffset = MaxSplitSliceEndOffset;
+        return;
+      }
+
+      // If the we have split slices and the next slice is after a gap and is
+      // not splittable immediately form an empty partition for the split
+      // slices up until the next slice begins.
+      if (!P.SplitTails.empty() && P.SI->beginOffset() != P.EndOffset &&
+          !P.SI->isSplittable()) {
+        P.BeginOffset = P.EndOffset;
+        P.EndOffset = P.SI->beginOffset();
+        return;
+      }
+    }
+
+    // OK, we need to consume new slices. Set the end offset based on the
+    // current slice, and step SJ past it. The beginning offset of the
+    // partition is the beginning offset of the next slice unless we have
+    // pre-existing split slices that are continuing, in which case we begin
+    // at the prior end offset.
+    P.BeginOffset = P.SplitTails.empty() ? P.SI->beginOffset() : P.EndOffset;
+    P.EndOffset = P.SI->endOffset();
+    ++P.SJ;
+
+    // There are two strategies to form a partition based on whether the
+    // partition starts with an unsplittable slice or a splittable slice.
+    if (!P.SI->isSplittable()) {
+      // When we're forming an unsplittable region, it must always start at
+      // the first slice and will extend through its end.
+      assert(P.BeginOffset == P.SI->beginOffset());
+
+      // Form a partition including all of the overlapping slices with this
+      // unsplittable slice.
+      while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) {
+        if (!P.SJ->isSplittable())
+          P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset());
+        ++P.SJ;
+      }
+
+      // We have a partition across a set of overlapping unsplittable
+      // partitions.
+      return;
+    }
+
+    // If we're starting with a splittable slice, then we need to form
+    // a synthetic partition spanning it and any other overlapping splittable
+    // splices.
+    assert(P.SI->isSplittable() && "Forming a splittable partition!");
+
+    // Collect all of the overlapping splittable slices.
+    while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset &&
+           P.SJ->isSplittable()) {
+      P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset());
+      ++P.SJ;
+    }
+
+    // Back upiP.EndOffset if we ended the span early when encountering an
+    // unsplittable slice. This synthesizes the early end offset of
+    // a partition spanning only splittable slices.
+    if (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) {
+      assert(!P.SJ->isSplittable());
+      P.EndOffset = P.SJ->beginOffset();
+    }
+  }
+
+public:
+  bool operator==(const partition_iterator &RHS) const {
+    assert(SE == RHS.SE &&
+           "End iterators don't match between compared partition iterators!");
+
+    // The observed positions of partitions is marked by the P.SI iterator and
+    // the emptiness of the split slices. The latter is only relevant when
+    // P.SI == SE, as the end iterator will additionally have an empty split
+    // slices list, but the prior may have the same P.SI and a tail of split
+    // slices.
+    if (P.SI == RHS.P.SI && P.SplitTails.empty() == RHS.P.SplitTails.empty()) {
+      assert(P.SJ == RHS.P.SJ &&
+             "Same set of slices formed two different sized partitions!");
+      assert(P.SplitTails.size() == RHS.P.SplitTails.size() &&
+             "Same slice position with differently sized non-empty split "
+             "slice tails!");
+      return true;
+    }
+    return false;
+  }
+
+  partition_iterator &operator++() {
+    advance();
+    return *this;
+  }
+
+  Partition &operator*() { return P; }
+};
+
+/// A forward range over the partitions of the alloca's slices.
+///
+/// This accesses an iterator range over the partitions of the alloca's
+/// slices. It computes these partitions on the fly based on the overlapping
+/// offsets of the slices and the ability to split them. It will visit "empty"
+/// partitions to cover regions of the alloca only accessed via split
+/// slices.
+iterator_range<AllocaSlices::partition_iterator> AllocaSlices::partitions() {
+  return make_range(partition_iterator(begin(), end()),
+                    partition_iterator(end(), end()));
+}
+
+static Value *foldSelectInst(SelectInst &SI) {
+  // If the condition being selected on is a constant or the same value is
+  // being selected between, fold the select. Yes this does (rarely) happen
+  // early on.
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(SI.getCondition()))
+    return SI.getOperand(1 + CI->isZero());
+  if (SI.getOperand(1) == SI.getOperand(2))
+    return SI.getOperand(1);
+
+  return nullptr;
+}
+
+/// A helper that folds a PHI node or a select.
+static Value *foldPHINodeOrSelectInst(Instruction &I) {
+  if (PHINode *PN = dyn_cast<PHINode>(&I)) {
+    // If PN merges together the same value, return that value.
+    return PN->hasConstantValue();
+  }
+  return foldSelectInst(cast<SelectInst>(I));
+}
+
+/// Builder for the alloca slices.
+///
+/// This class builds a set of alloca slices by recursively visiting the uses
+/// of an alloca and making a slice for each load and store at each offset.
+class AllocaSlices::SliceBuilder : public PtrUseVisitor<SliceBuilder> {
+  friend class PtrUseVisitor<SliceBuilder>;
+  friend class InstVisitor<SliceBuilder>;
+
+  using Base = PtrUseVisitor<SliceBuilder>;
+
+  const uint64_t AllocSize;
+  AllocaSlices &AS;
+
+  SmallDenseMap<Instruction *, unsigned> MemTransferSliceMap;
+  SmallDenseMap<Instruction *, uint64_t> PHIOrSelectSizes;
+
+  /// Set to de-duplicate dead instructions found in the use walk.
+  SmallPtrSet<Instruction *, 4> VisitedDeadInsts;
+
+public:
+  SliceBuilder(const DataLayout &DL, AllocaInst &AI, AllocaSlices &AS)
+      : PtrUseVisitor<SliceBuilder>(DL),
+        AllocSize(DL.getTypeAllocSize(AI.getAllocatedType()).getFixedValue()),
+        AS(AS) {}
+
+private:
+  void markAsDead(Instruction &I) {
+    if (VisitedDeadInsts.insert(&I).second)
+      AS.DeadUsers.push_back(&I);
+  }
+
+  void insertUse(Instruction &I, const APInt &Offset, uint64_t Size,
+                 bool IsSplittable = false) {
+    // Completely skip uses which have a zero size or start either before or
+    // past the end of the allocation.
+    if (Size == 0 || Offset.uge(AllocSize)) {
+      LLVM_DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @"
+                        << Offset
+                        << " which has zero size or starts outside of the "
+                        << AllocSize << " byte alloca:\n"
+                        << "    alloca: " << AS.AI << "\n"
+                        << "       use: " << I << "\n");
+      return markAsDead(I);
+    }
+
+    uint64_t BeginOffset = Offset.getZExtValue();
+    uint64_t EndOffset = BeginOffset + Size;
+
+    // Clamp the end offset to the end of the allocation. Note that this is
+    // formulated to handle even the case where "BeginOffset + Size" overflows.
+    // This may appear superficially to be something we could ignore entirely,
+    // but that is not so! There may be widened loads or PHI-node uses where
+    // some instructions are dead but not others. We can't completely ignore
+    // them, and so have to record at least the information here.
+    assert(AllocSize >= BeginOffset); // Established above.
+    if (Size > AllocSize - BeginOffset) {
+      LLVM_DEBUG(dbgs() << "WARNING: Clamping a " << Size << " byte use @"
+                        << Offset << " to remain within the " << AllocSize
+                        << " byte alloca:\n"
+                        << "    alloca: " << AS.AI << "\n"
+                        << "       use: " << I << "\n");
+      EndOffset = AllocSize;
+    }
+
+    AS.Slices.push_back(Slice(BeginOffset, EndOffset, U, IsSplittable));
+  }
+
+  void visitBitCastInst(BitCastInst &BC) {
+    if (BC.use_empty())
+      return markAsDead(BC);
+
+    return Base::visitBitCastInst(BC);
+  }
+
+  void visitAddrSpaceCastInst(AddrSpaceCastInst &ASC) {
+    if (ASC.use_empty())
+      return markAsDead(ASC);
+
+    return Base::visitAddrSpaceCastInst(ASC);
+  }
+
+  void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
+    if (GEPI.use_empty())
+      return markAsDead(GEPI);
+
+    if (SROAStrictInbounds && GEPI.isInBounds()) {
+      // FIXME: This is a manually un-factored variant of the basic code inside
+      // of GEPs with checking of the inbounds invariant specified in the
+      // langref in a very strict sense. If we ever want to enable
+      // SROAStrictInbounds, this code should be factored cleanly into
+      // PtrUseVisitor, but it is easier to experiment with SROAStrictInbounds
+      // by writing out the code here where we have the underlying allocation
+      // size readily available.
+      APInt GEPOffset = Offset;
+      const DataLayout &DL = GEPI.getModule()->getDataLayout();
+      for (gep_type_iterator GTI = gep_type_begin(GEPI),
+                             GTE = gep_type_end(GEPI);
+           GTI != GTE; ++GTI) {
+        ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
+        if (!OpC)
+          break;
+
+        // Handle a struct index, which adds its field offset to the pointer.
+        if (StructType *STy = GTI.getStructTypeOrNull()) {
+          unsigned ElementIdx = OpC->getZExtValue();
+          const StructLayout *SL = DL.getStructLayout(STy);
+          GEPOffset +=
+              APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx));
+        } else {
+          // For array or vector indices, scale the index by the size of the
+          // type.
+          APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth());
+          GEPOffset +=
+              Index *
+              APInt(Offset.getBitWidth(),
+                    DL.getTypeAllocSize(GTI.getIndexedType()).getFixedValue());
+        }
+
+        // If this index has computed an intermediate pointer which is not
+        // inbounds, then the result of the GEP is a poison value and we can
+        // delete it and all uses.
+        if (GEPOffset.ugt(AllocSize))
+          return markAsDead(GEPI);
+      }
+    }
+
+    return Base::visitGetElementPtrInst(GEPI);
+  }
+
+  void handleLoadOrStore(Type *Ty, Instruction &I, const APInt &Offset,
+                         uint64_t Size, bool IsVolatile) {
+    // We allow splitting of non-volatile loads and stores where the type is an
+    // integer type. These may be used to implement 'memcpy' or other "transfer
+    // of bits" patterns.
+    bool IsSplittable =
+        Ty->isIntegerTy() && !IsVolatile && DL.typeSizeEqualsStoreSize(Ty);
+
+    insertUse(I, Offset, Size, IsSplittable);
+  }
+
+  void visitLoadInst(LoadInst &LI) {
+    assert((!LI.isSimple() || LI.getType()->isSingleValueType()) &&
+           "All simple FCA loads should have been pre-split");
+
+    if (!IsOffsetKnown)
+      return PI.setAborted(&LI);
+
+    if (isa<ScalableVectorType>(LI.getType()))
+      return PI.setAborted(&LI);
+
+    uint64_t Size = DL.getTypeStoreSize(LI.getType()).getFixedValue();
+    return handleLoadOrStore(LI.getType(), LI, Offset, Size, LI.isVolatile());
+  }
+
+  void visitStoreInst(StoreInst &SI) {
+    Value *ValOp = SI.getValueOperand();
+    if (ValOp == *U)
+      return PI.setEscapedAndAborted(&SI);
+    if (!IsOffsetKnown)
+      return PI.setAborted(&SI);
+
+    if (isa<ScalableVectorType>(ValOp->getType()))
+      return PI.setAborted(&SI);
+
+    uint64_t Size = DL.getTypeStoreSize(ValOp->getType()).getFixedValue();
+
+    // If this memory access can be shown to *statically* extend outside the
+    // bounds of the allocation, it's behavior is undefined, so simply
+    // ignore it. Note that this is more strict than the generic clamping
+    // behavior of insertUse. We also try to handle cases which might run the
+    // risk of overflow.
+    // FIXME: We should instead consider the pointer to have escaped if this
+    // function is being instrumented for addressing bugs or race conditions.
+    if (Size > AllocSize || Offset.ugt(AllocSize - Size)) {
+      LLVM_DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte store @"
+                        << Offset << " which extends past the end of the "
+                        << AllocSize << " byte alloca:\n"
+                        << "    alloca: " << AS.AI << "\n"
+                        << "       use: " << SI << "\n");
+      return markAsDead(SI);
+    }
+
+    assert((!SI.isSimple() || ValOp->getType()->isSingleValueType()) &&
+           "All simple FCA stores should have been pre-split");
+    handleLoadOrStore(ValOp->getType(), SI, Offset, Size, SI.isVolatile());
+  }
+
+  void visitMemSetInst(MemSetInst &II) {
+    assert(II.getRawDest() == *U && "Pointer use is not the destination?");
+    ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
+    if ((Length && Length->getValue() == 0) ||
+        (IsOffsetKnown && Offset.uge(AllocSize)))
+      // Zero-length mem transfer intrinsics can be ignored entirely.
+      return markAsDead(II);
+
+    if (!IsOffsetKnown)
+      return PI.setAborted(&II);
+
+    insertUse(II, Offset, Length ? Length->getLimitedValue()
+                                 : AllocSize - Offset.getLimitedValue(),
+              (bool)Length);
+  }
+
+  void visitMemTransferInst(MemTransferInst &II) {
+    ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
+    if (Length && Length->getValue() == 0)
+      // Zero-length mem transfer intrinsics can be ignored entirely.
+      return markAsDead(II);
+
+    // Because we can visit these intrinsics twice, also check to see if the
+    // first time marked this instruction as dead. If so, skip it.
+    if (VisitedDeadInsts.count(&II))
+      return;
+
+    if (!IsOffsetKnown)
+      return PI.setAborted(&II);
+
+    // This side of the transfer is completely out-of-bounds, and so we can
+    // nuke the entire transfer. However, we also need to nuke the other side
+    // if already added to our partitions.
+    // FIXME: Yet another place we really should bypass this when
+    // instrumenting for ASan.
+    if (Offset.uge(AllocSize)) {
+      SmallDenseMap<Instruction *, unsigned>::iterator MTPI =
+          MemTransferSliceMap.find(&II);
+      if (MTPI != MemTransferSliceMap.end())
+        AS.Slices[MTPI->second].kill();
+      return markAsDead(II);
+    }
+
+    uint64_t RawOffset = Offset.getLimitedValue();
+    uint64_t Size = Length ? Length->getLimitedValue() : AllocSize - RawOffset;
+
+    // Check for the special case where the same exact value is used for both
+    // source and dest.
+    if (*U == II.getRawDest() && *U == II.getRawSource()) {
+      // For non-volatile transfers this is a no-op.
+      if (!II.isVolatile())
+        return markAsDead(II);
+
+      return insertUse(II, Offset, Size, /*IsSplittable=*/false);
+    }
+
+    // If we have seen both source and destination for a mem transfer, then
+    // they both point to the same alloca.
+    bool Inserted;
+    SmallDenseMap<Instruction *, unsigned>::iterator MTPI;
+    std::tie(MTPI, Inserted) =
+        MemTransferSliceMap.insert(std::make_pair(&II, AS.Slices.size()));
+    unsigned PrevIdx = MTPI->second;
+    if (!Inserted) {
+      Slice &PrevP = AS.Slices[PrevIdx];
+
+      // Check if the begin offsets match and this is a non-volatile transfer.
+      // In that case, we can completely elide the transfer.
+      if (!II.isVolatile() && PrevP.beginOffset() == RawOffset) {
+        PrevP.kill();
+        return markAsDead(II);
+      }
+
+      // Otherwise we have an offset transfer within the same alloca. We can't
+      // split those.
+      PrevP.makeUnsplittable();
+    }
+
+    // Insert the use now that we've fixed up the splittable nature.
+    insertUse(II, Offset, Size, /*IsSplittable=*/Inserted && Length);
+
+    // Check that we ended up with a valid index in the map.
+    assert(AS.Slices[PrevIdx].getUse()->getUser() == &II &&
+           "Map index doesn't point back to a slice with this user.");
+  }
+
+  // Disable SRoA for any intrinsics except for lifetime invariants and
+  // invariant group.
+  // FIXME: What about debug intrinsics? This matches old behavior, but
+  // doesn't make sense.
+  void visitIntrinsicInst(IntrinsicInst &II) {
+    if (II.isDroppable()) {
+      AS.DeadUseIfPromotable.push_back(U);
+      return;
+    }
+
+    if (!IsOffsetKnown)
+      return PI.setAborted(&II);
+
+    if (II.isLifetimeStartOrEnd()) {
+      ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0));
+      uint64_t Size = std::min(AllocSize - Offset.getLimitedValue(),
+                               Length->getLimitedValue());
+      insertUse(II, Offset, Size, true);
+      return;
+    }
+
+    if (II.isLaunderOrStripInvariantGroup()) {
+      enqueueUsers(II);
+      return;
+    }
+
+    Base::visitIntrinsicInst(II);
+  }
+
+  Instruction *hasUnsafePHIOrSelectUse(Instruction *Root, uint64_t &Size) {
+    // We consider any PHI or select that results in a direct load or store of
+    // the same offset to be a viable use for slicing purposes. These uses
+    // are considered unsplittable and the size is the maximum loaded or stored
+    // size.
+    SmallPtrSet<Instruction *, 4> Visited;
+    SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
+    Visited.insert(Root);
+    Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
+    const DataLayout &DL = Root->getModule()->getDataLayout();
+    // If there are no loads or stores, the access is dead. We mark that as
+    // a size zero access.
+    Size = 0;
+    do {
+      Instruction *I, *UsedI;
+      std::tie(UsedI, I) = Uses.pop_back_val();
+
+      if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+        Size =
+            std::max(Size, DL.getTypeStoreSize(LI->getType()).getFixedValue());
+        continue;
+      }
+      if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+        Value *Op = SI->getOperand(0);
+        if (Op == UsedI)
+          return SI;
+        Size =
+            std::max(Size, DL.getTypeStoreSize(Op->getType()).getFixedValue());
+        continue;
+      }
+
+      if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
+        if (!GEP->hasAllZeroIndices())
+          return GEP;
+      } else if (!isa<BitCastInst>(I) && !isa<PHINode>(I) &&
+                 !isa<SelectInst>(I) && !isa<AddrSpaceCastInst>(I)) {
+        return I;
+      }
+
+      for (User *U : I->users())
+        if (Visited.insert(cast<Instruction>(U)).second)
+          Uses.push_back(std::make_pair(I, cast<Instruction>(U)));
+    } while (!Uses.empty());
+
+    return nullptr;
+  }
+
+  void visitPHINodeOrSelectInst(Instruction &I) {
+    assert(isa<PHINode>(I) || isa<SelectInst>(I));
+    if (I.use_empty())
+      return markAsDead(I);
+
+    // If this is a PHI node before a catchswitch, we cannot insert any non-PHI
+    // instructions in this BB, which may be required during rewriting. Bail out
+    // on these cases.
+    if (isa<PHINode>(I) &&
+        I.getParent()->getFirstInsertionPt() == I.getParent()->end())
+      return PI.setAborted(&I);
+
+    // TODO: We could use simplifyInstruction here to fold PHINodes and
+    // SelectInsts. However, doing so requires to change the current
+    // dead-operand-tracking mechanism. For instance, suppose neither loading
+    // from %U nor %other traps. Then "load (select undef, %U, %other)" does not
+    // trap either.  However, if we simply replace %U with undef using the
+    // current dead-operand-tracking mechanism, "load (select undef, undef,
+    // %other)" may trap because the select may return the first operand
+    // "undef".
+    if (Value *Result = foldPHINodeOrSelectInst(I)) {
+      if (Result == *U)
+        // If the result of the constant fold will be the pointer, recurse
+        // through the PHI/select as if we had RAUW'ed it.
+        enqueueUsers(I);
+      else
+        // Otherwise the operand to the PHI/select is dead, and we can replace
+        // it with poison.
+        AS.DeadOperands.push_back(U);
+
+      return;
+    }
+
+    if (!IsOffsetKnown)
+      return PI.setAborted(&I);
+
+    // See if we already have computed info on this node.
+    uint64_t &Size = PHIOrSelectSizes[&I];
+    if (!Size) {
+      // This is a new PHI/Select, check for an unsafe use of it.
+      if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&I, Size))
+        return PI.setAborted(UnsafeI);
+    }
+
+    // For PHI and select operands outside the alloca, we can't nuke the entire
+    // phi or select -- the other side might still be relevant, so we special
+    // case them here and use a separate structure to track the operands
+    // themselves which should be replaced with poison.
+    // FIXME: This should instead be escaped in the event we're instrumenting
+    // for address sanitization.
+    if (Offset.uge(AllocSize)) {
+      AS.DeadOperands.push_back(U);
+      return;
+    }
+
+    insertUse(I, Offset, Size);
+  }
+
+  void visitPHINode(PHINode &PN) { visitPHINodeOrSelectInst(PN); }
+
+  void visitSelectInst(SelectInst &SI) { visitPHINodeOrSelectInst(SI); }
+
+  /// Disable SROA entirely if there are unhandled users of the alloca.
+  void visitInstruction(Instruction &I) { PI.setAborted(&I); }
+};
+
+AllocaSlices::AllocaSlices(const DataLayout &DL, AllocaInst &AI)
+    :
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+      AI(AI),
+#endif
+      PointerEscapingInstr(nullptr) {
+  SliceBuilder PB(DL, AI, *this);
+  SliceBuilder::PtrInfo PtrI = PB.visitPtr(AI);
+  if (PtrI.isEscaped() || PtrI.isAborted()) {
+    // FIXME: We should sink the escape vs. abort info into the caller nicely,
+    // possibly by just storing the PtrInfo in the AllocaSlices.
+    PointerEscapingInstr = PtrI.getEscapingInst() ? PtrI.getEscapingInst()
+                                                  : PtrI.getAbortingInst();
+    assert(PointerEscapingInstr && "Did not track a bad instruction");
+    return;
+  }
+
+  llvm::erase_if(Slices, [](const Slice &S) { return S.isDead(); });
+
+  // Sort the uses. This arranges for the offsets to be in ascending order,
+  // and the sizes to be in descending order.
+  llvm::stable_sort(Slices);
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+
+void AllocaSlices::print(raw_ostream &OS, const_iterator I,
+                         StringRef Indent) const {
+  printSlice(OS, I, Indent);
+  OS << "\n";
+  printUse(OS, I, Indent);
+}
+
+void AllocaSlices::printSlice(raw_ostream &OS, const_iterator I,
+                              StringRef Indent) const {
+  OS << Indent << "[" << I->beginOffset() << "," << I->endOffset() << ")"
+     << " slice #" << (I - begin())
+     << (I->isSplittable() ? " (splittable)" : "");
+}
+
+void AllocaSlices::printUse(raw_ostream &OS, const_iterator I,
+                            StringRef Indent) const {
+  OS << Indent << "  used by: " << *I->getUse()->getUser() << "\n";
+}
+
+void AllocaSlices::print(raw_ostream &OS) const {
+  if (PointerEscapingInstr) {
+    OS << "Can't analyze slices for alloca: " << AI << "\n"
+       << "  A pointer to this alloca escaped by:\n"
+       << "  " << *PointerEscapingInstr << "\n";
+    return;
+  }
+
+  OS << "Slices of alloca: " << AI << "\n";
+  for (const_iterator I = begin(), E = end(); I != E; ++I)
+    print(OS, I);
+}
+
+LLVM_DUMP_METHOD void AllocaSlices::dump(const_iterator I) const {
+  print(dbgs(), I);
+}
+LLVM_DUMP_METHOD void AllocaSlices::dump() const { print(dbgs()); }
+
+#endif // !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+
+/// Walk the range of a partitioning looking for a common type to cover this
+/// sequence of slices.
+static std::pair<Type *, IntegerType *>
+findCommonType(AllocaSlices::const_iterator B, AllocaSlices::const_iterator E,
+               uint64_t EndOffset) {
+  Type *Ty = nullptr;
+  bool TyIsCommon = true;
+  IntegerType *ITy = nullptr;
+
+  // Note that we need to look at *every* alloca slice's Use to ensure we
+  // always get consistent results regardless of the order of slices.
+  for (AllocaSlices::const_iterator I = B; I != E; ++I) {
+    Use *U = I->getUse();
+    if (isa<IntrinsicInst>(*U->getUser()))
+      continue;
+    if (I->beginOffset() != B->beginOffset() || I->endOffset() != EndOffset)
+      continue;
+
+    Type *UserTy = nullptr;
+    if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
+      UserTy = LI->getType();
+    } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
+      UserTy = SI->getValueOperand()->getType();
+    }
+
+    if (IntegerType *UserITy = dyn_cast_or_null<IntegerType>(UserTy)) {
+      // If the type is larger than the partition, skip it. We only encounter
+      // this for split integer operations where we want to use the type of the
+      // entity causing the split. Also skip if the type is not a byte width
+      // multiple.
+      if (UserITy->getBitWidth() % 8 != 0 ||
+          UserITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
+        continue;
+
+      // Track the largest bitwidth integer type used in this way in case there
+      // is no common type.
+      if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth())
+        ITy = UserITy;
+    }
+
+    // To avoid depending on the order of slices, Ty and TyIsCommon must not
+    // depend on types skipped above.
+    if (!UserTy || (Ty && Ty != UserTy))
+      TyIsCommon = false; // Give up on anything but an iN type.
+    else
+      Ty = UserTy;
+  }
+
+  return {TyIsCommon ? Ty : nullptr, ITy};
+}
+
+/// PHI instructions that use an alloca and are subsequently loaded can be
+/// rewritten to load both input pointers in the pred blocks and then PHI the
+/// results, allowing the load of the alloca to be promoted.
+/// From this:
+///   %P2 = phi [i32* %Alloca, i32* %Other]
+///   %V = load i32* %P2
+/// to:
+///   %V1 = load i32* %Alloca      -> will be mem2reg'd
+///   ...
+///   %V2 = load i32* %Other
+///   ...
+///   %V = phi [i32 %V1, i32 %V2]
+///
+/// We can do this to a select if its only uses are loads and if the operands
+/// to the select can be loaded unconditionally.
+///
+/// FIXME: This should be hoisted into a generic utility, likely in
+/// Transforms/Util/Local.h
+static bool isSafePHIToSpeculate(PHINode &PN) {
+  const DataLayout &DL = PN.getModule()->getDataLayout();
+
+  // For now, we can only do this promotion if the load is in the same block
+  // as the PHI, and if there are no stores between the phi and load.
+  // TODO: Allow recursive phi users.
+  // TODO: Allow stores.
+  BasicBlock *BB = PN.getParent();
+  Align MaxAlign;
+  uint64_t APWidth = DL.getIndexTypeSizeInBits(PN.getType());
+  Type *LoadType = nullptr;
+  for (User *U : PN.users()) {
+    LoadInst *LI = dyn_cast<LoadInst>(U);
+    if (!LI || !LI->isSimple())
+      return false;
+
+    // For now we only allow loads in the same block as the PHI.  This is
+    // a common case that happens when instcombine merges two loads through
+    // a PHI.
+    if (LI->getParent() != BB)
+      return false;
+
+    if (LoadType) {
+      if (LoadType != LI->getType())
+        return false;
+    } else {
+      LoadType = LI->getType();
+    }
+
+    // Ensure that there are no instructions between the PHI and the load that
+    // could store.
+    for (BasicBlock::iterator BBI(PN); &*BBI != LI; ++BBI)
+      if (BBI->mayWriteToMemory())
+        return false;
+
+    MaxAlign = std::max(MaxAlign, LI->getAlign());
+  }
+
+  if (!LoadType)
+    return false;
+
+  APInt LoadSize =
+      APInt(APWidth, DL.getTypeStoreSize(LoadType).getFixedValue());
+
+  // We can only transform this if it is safe to push the loads into the
+  // predecessor blocks. The only thing to watch out for is that we can't put
+  // a possibly trapping load in the predecessor if it is a critical edge.
+  for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
+    Instruction *TI = PN.getIncomingBlock(Idx)->getTerminator();
+    Value *InVal = PN.getIncomingValue(Idx);
+
+    // If the value is produced by the terminator of the predecessor (an
+    // invoke) or it has side-effects, there is no valid place to put a load
+    // in the predecessor.
+    if (TI == InVal || TI->mayHaveSideEffects())
+      return false;
+
+    // If the predecessor has a single successor, then the edge isn't
+    // critical.
+    if (TI->getNumSuccessors() == 1)
+      continue;
+
+    // If this pointer is always safe to load, or if we can prove that there
+    // is already a load in the block, then we can move the load to the pred
+    // block.
+    if (isSafeToLoadUnconditionally(InVal, MaxAlign, LoadSize, DL, TI))
+      continue;
+
+    return false;
+  }
+
+  return true;
+}
+
+static void speculatePHINodeLoads(IRBuilderTy &IRB, PHINode &PN) {
+  LLVM_DEBUG(dbgs() << "    original: " << PN << "\n");
+
+  LoadInst *SomeLoad = cast<LoadInst>(PN.user_back());
+  Type *LoadTy = SomeLoad->getType();
+  IRB.SetInsertPoint(&PN);
+  PHINode *NewPN = IRB.CreatePHI(LoadTy, PN.getNumIncomingValues(),
+                                 PN.getName() + ".sroa.speculated");
+
+  // Get the AA tags and alignment to use from one of the loads. It does not
+  // matter which one we get and if any differ.
+  AAMDNodes AATags = SomeLoad->getAAMetadata();
+  Align Alignment = SomeLoad->getAlign();
+
+  // Rewrite all loads of the PN to use the new PHI.
+  while (!PN.use_empty()) {
+    LoadInst *LI = cast<LoadInst>(PN.user_back());
+    LI->replaceAllUsesWith(NewPN);
+    LI->eraseFromParent();
+  }
+
+  // Inject loads into all of the pred blocks.
+  DenseMap<BasicBlock*, Value*> InjectedLoads;
+  for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
+    BasicBlock *Pred = PN.getIncomingBlock(Idx);
+    Value *InVal = PN.getIncomingValue(Idx);
+
+    // A PHI node is allowed to have multiple (duplicated) entries for the same
+    // basic block, as long as the value is the same. So if we already injected
+    // a load in the predecessor, then we should reuse the same load for all
+    // duplicated entries.
+    if (Value* V = InjectedLoads.lookup(Pred)) {
+      NewPN->addIncoming(V, Pred);
+      continue;
+    }
+
+    Instruction *TI = Pred->getTerminator();
+    IRB.SetInsertPoint(TI);
+
+    LoadInst *Load = IRB.CreateAlignedLoad(
+        LoadTy, InVal, Alignment,
+        (PN.getName() + ".sroa.speculate.load." + Pred->getName()));
+    ++NumLoadsSpeculated;
+    if (AATags)
+      Load->setAAMetadata(AATags);
+    NewPN->addIncoming(Load, Pred);
+    InjectedLoads[Pred] = Load;
+  }
+
+  LLVM_DEBUG(dbgs() << "          speculated to: " << *NewPN << "\n");
+  PN.eraseFromParent();
+}
+
+sroa::SelectHandSpeculativity &
+sroa::SelectHandSpeculativity::setAsSpeculatable(bool isTrueVal) {
+  if (isTrueVal)
+    Bitfield::set<sroa::SelectHandSpeculativity::TrueVal>(Storage, true);
+  else
+    Bitfield::set<sroa::SelectHandSpeculativity::FalseVal>(Storage, true);
+  return *this;
+}
+
+bool sroa::SelectHandSpeculativity::isSpeculatable(bool isTrueVal) const {
+  return isTrueVal
+             ? Bitfield::get<sroa::SelectHandSpeculativity::TrueVal>(Storage)
+             : Bitfield::get<sroa::SelectHandSpeculativity::FalseVal>(Storage);
+}
+
+bool sroa::SelectHandSpeculativity::areAllSpeculatable() const {
+  return isSpeculatable(/*isTrueVal=*/true) &&
+         isSpeculatable(/*isTrueVal=*/false);
+}
+
+bool sroa::SelectHandSpeculativity::areAnySpeculatable() const {
+  return isSpeculatable(/*isTrueVal=*/true) ||
+         isSpeculatable(/*isTrueVal=*/false);
+}
+bool sroa::SelectHandSpeculativity::areNoneSpeculatable() const {
+  return !areAnySpeculatable();
+}
+
+static sroa::SelectHandSpeculativity
+isSafeLoadOfSelectToSpeculate(LoadInst &LI, SelectInst &SI, bool PreserveCFG) {
+  assert(LI.isSimple() && "Only for simple loads");
+  sroa::SelectHandSpeculativity Spec;
+
+  const DataLayout &DL = SI.getModule()->getDataLayout();
+  for (Value *Value : {SI.getTrueValue(), SI.getFalseValue()})
+    if (isSafeToLoadUnconditionally(Value, LI.getType(), LI.getAlign(), DL,
+                                    &LI))
+      Spec.setAsSpeculatable(/*isTrueVal=*/Value == SI.getTrueValue());
+    else if (PreserveCFG)
+      return Spec;
+
+  return Spec;
+}
+
+std::optional<sroa::RewriteableMemOps>
+SROAPass::isSafeSelectToSpeculate(SelectInst &SI, bool PreserveCFG) {
+  RewriteableMemOps Ops;
+
+  for (User *U : SI.users()) {
+    if (auto *BC = dyn_cast<BitCastInst>(U); BC && BC->hasOneUse())
+      U = *BC->user_begin();
+
+    if (auto *Store = dyn_cast<StoreInst>(U)) {
+      // Note that atomic stores can be transformed; atomic semantics do not
+      // have any meaning for a local alloca. Stores are not speculatable,
+      // however, so if we can't turn it into a predicated store, we are done.
+      if (Store->isVolatile() || PreserveCFG)
+        return {}; // Give up on this `select`.
+      Ops.emplace_back(Store);
+      continue;
+    }
+
+    auto *LI = dyn_cast<LoadInst>(U);
+
+    // Note that atomic loads can be transformed;
+    // atomic semantics do not have any meaning for a local alloca.
+    if (!LI || LI->isVolatile())
+      return {}; // Give up on this `select`.
+
+    PossiblySpeculatableLoad Load(LI);
+    if (!LI->isSimple()) {
+      // If the `load` is not simple, we can't speculatively execute it,
+      // but we could handle this via a CFG modification. But can we?
+      if (PreserveCFG)
+        return {}; // Give up on this `select`.
+      Ops.emplace_back(Load);
+      continue;
+    }
+
+    sroa::SelectHandSpeculativity Spec =
+        isSafeLoadOfSelectToSpeculate(*LI, SI, PreserveCFG);
+    if (PreserveCFG && !Spec.areAllSpeculatable())
+      return {}; // Give up on this `select`.
+
+    Load.setInt(Spec);
+    Ops.emplace_back(Load);
+  }
+
+  return Ops;
+}
+
+static void speculateSelectInstLoads(SelectInst &SI, LoadInst &LI,
+                                     IRBuilderTy &IRB) {
+  LLVM_DEBUG(dbgs() << "    original load: " << SI << "\n");
+
+  Value *TV = SI.getTrueValue();
+  Value *FV = SI.getFalseValue();
+  // Replace the given load of the select with a select of two loads.
+
+  assert(LI.isSimple() && "We only speculate simple loads");
+
+  IRB.SetInsertPoint(&LI);
+
+  if (auto *TypedPtrTy = LI.getPointerOperandType();
+      !TypedPtrTy->isOpaquePointerTy() && SI.getType() != TypedPtrTy) {
+    TV = IRB.CreateBitOrPointerCast(TV, TypedPtrTy, "");
+    FV = IRB.CreateBitOrPointerCast(FV, TypedPtrTy, "");
+  }
+
+  LoadInst *TL =
+      IRB.CreateAlignedLoad(LI.getType(), TV, LI.getAlign(),
+                            LI.getName() + ".sroa.speculate.load.true");
+  LoadInst *FL =
+      IRB.CreateAlignedLoad(LI.getType(), FV, LI.getAlign(),
+                            LI.getName() + ".sroa.speculate.load.false");
+  NumLoadsSpeculated += 2;
+
+  // Transfer alignment and AA info if present.
+  TL->setAlignment(LI.getAlign());
+  FL->setAlignment(LI.getAlign());
+
+  AAMDNodes Tags = LI.getAAMetadata();
+  if (Tags) {
+    TL->setAAMetadata(Tags);
+    FL->setAAMetadata(Tags);
+  }
+
+  Value *V = IRB.CreateSelect(SI.getCondition(), TL, FL,
+                              LI.getName() + ".sroa.speculated");
+
+  LLVM_DEBUG(dbgs() << "          speculated to: " << *V << "\n");
+  LI.replaceAllUsesWith(V);
+}
+
+template <typename T>
+static void rewriteMemOpOfSelect(SelectInst &SI, T &I,
+                                 sroa::SelectHandSpeculativity Spec,
+                                 DomTreeUpdater &DTU) {
+  assert((isa<LoadInst>(I) || isa<StoreInst>(I)) && "Only for load and store!");
+  LLVM_DEBUG(dbgs() << "    original mem op: " << I << "\n");
+  BasicBlock *Head = I.getParent();
+  Instruction *ThenTerm = nullptr;
+  Instruction *ElseTerm = nullptr;
+  if (Spec.areNoneSpeculatable())
+    SplitBlockAndInsertIfThenElse(SI.getCondition(), &I, &ThenTerm, &ElseTerm,
+                                  SI.getMetadata(LLVMContext::MD_prof), &DTU);
+  else {
+    SplitBlockAndInsertIfThen(SI.getCondition(), &I, /*Unreachable=*/false,
+                              SI.getMetadata(LLVMContext::MD_prof), &DTU,
+                              /*LI=*/nullptr, /*ThenBlock=*/nullptr);
+    if (Spec.isSpeculatable(/*isTrueVal=*/true))
+      cast<BranchInst>(Head->getTerminator())->swapSuccessors();
+  }
+  auto *HeadBI = cast<BranchInst>(Head->getTerminator());
+  Spec = {}; // Do not use `Spec` beyond this point.
+  BasicBlock *Tail = I.getParent();
+  Tail->setName(Head->getName() + ".cont");
+  PHINode *PN;
+  if (isa<LoadInst>(I))
+    PN = PHINode::Create(I.getType(), 2, "", &I);
+  for (BasicBlock *SuccBB : successors(Head)) {
+    bool IsThen = SuccBB == HeadBI->getSuccessor(0);
+    int SuccIdx = IsThen ? 0 : 1;
+    auto *NewMemOpBB = SuccBB == Tail ? Head : SuccBB;
+    if (NewMemOpBB != Head) {
+      NewMemOpBB->setName(Head->getName() + (IsThen ? ".then" : ".else"));
+      if (isa<LoadInst>(I))
+        ++NumLoadsPredicated;
+      else
+        ++NumStoresPredicated;
+    } else
+      ++NumLoadsSpeculated;
+    auto &CondMemOp = cast<T>(*I.clone());
+    CondMemOp.insertBefore(NewMemOpBB->getTerminator());
+    Value *Ptr = SI.getOperand(1 + SuccIdx);
+    if (auto *PtrTy = Ptr->getType();
+        !PtrTy->isOpaquePointerTy() &&
+        PtrTy != CondMemOp.getPointerOperandType())
+      Ptr = BitCastInst::CreatePointerBitCastOrAddrSpaceCast(
+          Ptr, CondMemOp.getPointerOperandType(), "", &CondMemOp);
+    CondMemOp.setOperand(I.getPointerOperandIndex(), Ptr);
+    if (isa<LoadInst>(I)) {
+      CondMemOp.setName(I.getName() + (IsThen ? ".then" : ".else") + ".val");
+      PN->addIncoming(&CondMemOp, NewMemOpBB);
+    } else
+      LLVM_DEBUG(dbgs() << "                 to: " << CondMemOp << "\n");
+  }
+  if (isa<LoadInst>(I)) {
+    PN->takeName(&I);
+    LLVM_DEBUG(dbgs() << "          to: " << *PN << "\n");
+    I.replaceAllUsesWith(PN);
+  }
+}
+
+static void rewriteMemOpOfSelect(SelectInst &SelInst, Instruction &I,
+                                 sroa::SelectHandSpeculativity Spec,
+                                 DomTreeUpdater &DTU) {
+  if (auto *LI = dyn_cast<LoadInst>(&I))
+    rewriteMemOpOfSelect(SelInst, *LI, Spec, DTU);
+  else if (auto *SI = dyn_cast<StoreInst>(&I))
+    rewriteMemOpOfSelect(SelInst, *SI, Spec, DTU);
+  else
+    llvm_unreachable_internal("Only for load and store.");
+}
+
+static bool rewriteSelectInstMemOps(SelectInst &SI,
+                                    const sroa::RewriteableMemOps &Ops,
+                                    IRBuilderTy &IRB, DomTreeUpdater *DTU) {
+  bool CFGChanged = false;
+  LLVM_DEBUG(dbgs() << "    original select: " << SI << "\n");
+
+  for (const RewriteableMemOp &Op : Ops) {
+    sroa::SelectHandSpeculativity Spec;
+    Instruction *I;
+    if (auto *const *US = std::get_if<UnspeculatableStore>(&Op)) {
+      I = *US;
+    } else {
+      auto PSL = std::get<PossiblySpeculatableLoad>(Op);
+      I = PSL.getPointer();
+      Spec = PSL.getInt();
+    }
+    if (Spec.areAllSpeculatable()) {
+      speculateSelectInstLoads(SI, cast<LoadInst>(*I), IRB);
+    } else {
+      assert(DTU && "Should not get here when not allowed to modify the CFG!");
+      rewriteMemOpOfSelect(SI, *I, Spec, *DTU);
+      CFGChanged = true;
+    }
+    I->eraseFromParent();
+  }
+
+  for (User *U : make_early_inc_range(SI.users()))
+    cast<BitCastInst>(U)->eraseFromParent();
+  SI.eraseFromParent();
+  return CFGChanged;
+}
+
+/// Build a GEP out of a base pointer and indices.
+///
+/// This will return the BasePtr if that is valid, or build a new GEP
+/// instruction using the IRBuilder if GEP-ing is needed.
+static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
+                       SmallVectorImpl<Value *> &Indices,
+                       const Twine &NamePrefix) {
+  if (Indices.empty())
+    return BasePtr;
+
+  // A single zero index is a no-op, so check for this and avoid building a GEP
+  // in that case.
+  if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero())
+    return BasePtr;
+
+  // buildGEP() is only called for non-opaque pointers.
+  return IRB.CreateInBoundsGEP(
+      BasePtr->getType()->getNonOpaquePointerElementType(), BasePtr, Indices,
+      NamePrefix + "sroa_idx");
+}
+
+/// Get a natural GEP off of the BasePtr walking through Ty toward
+/// TargetTy without changing the offset of the pointer.
+///
+/// This routine assumes we've already established a properly offset GEP with
+/// Indices, and arrived at the Ty type. The goal is to continue to GEP with
+/// zero-indices down through type layers until we find one the same as
+/// TargetTy. If we can't find one with the same type, we at least try to use
+/// one with the same size. If none of that works, we just produce the GEP as
+/// indicated by Indices to have the correct offset.
+static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
+                                    Value *BasePtr, Type *Ty, Type *TargetTy,
+                                    SmallVectorImpl<Value *> &Indices,
+                                    const Twine &NamePrefix) {
+  if (Ty == TargetTy)
+    return buildGEP(IRB, BasePtr, Indices, NamePrefix);
+
+  // Offset size to use for the indices.
+  unsigned OffsetSize = DL.getIndexTypeSizeInBits(BasePtr->getType());
+
+  // See if we can descend into a struct and locate a field with the correct
+  // type.
+  unsigned NumLayers = 0;
+  Type *ElementTy = Ty;
+  do {
+    if (ElementTy->isPointerTy())
+      break;
+
+    if (ArrayType *ArrayTy = dyn_cast<ArrayType>(ElementTy)) {
+      ElementTy = ArrayTy->getElementType();
+      Indices.push_back(IRB.getIntN(OffsetSize, 0));
+    } else if (VectorType *VectorTy = dyn_cast<VectorType>(ElementTy)) {
+      ElementTy = VectorTy->getElementType();
+      Indices.push_back(IRB.getInt32(0));
+    } else if (StructType *STy = dyn_cast<StructType>(ElementTy)) {
+      if (STy->element_begin() == STy->element_end())
+        break; // Nothing left to descend into.
+      ElementTy = *STy->element_begin();
+      Indices.push_back(IRB.getInt32(0));
+    } else {
+      break;
+    }
+    ++NumLayers;
+  } while (ElementTy != TargetTy);
+  if (ElementTy != TargetTy)
+    Indices.erase(Indices.end() - NumLayers, Indices.end());
+
+  return buildGEP(IRB, BasePtr, Indices, NamePrefix);
+}
+
+/// Get a natural GEP from a base pointer to a particular offset and
+/// resulting in a particular type.
+///
+/// The goal is to produce a "natural" looking GEP that works with the existing
+/// composite types to arrive at the appropriate offset and element type for
+/// a pointer. TargetTy is the element type the returned GEP should point-to if
+/// possible. We recurse by decreasing Offset, adding the appropriate index to
+/// Indices, and setting Ty to the result subtype.
+///
+/// If no natural GEP can be constructed, this function returns null.
+static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
+                                      Value *Ptr, APInt Offset, Type *TargetTy,
+                                      SmallVectorImpl<Value *> &Indices,
+                                      const Twine &NamePrefix) {
+  PointerType *Ty = cast<PointerType>(Ptr->getType());
+
+  // Don't consider any GEPs through an i8* as natural unless the TargetTy is
+  // an i8.
+  if (Ty == IRB.getInt8PtrTy(Ty->getAddressSpace()) && TargetTy->isIntegerTy(8))
+    return nullptr;
+
+  Type *ElementTy = Ty->getNonOpaquePointerElementType();
+  if (!ElementTy->isSized())
+    return nullptr; // We can't GEP through an unsized element.
+
+  SmallVector<APInt> IntIndices = DL.getGEPIndicesForOffset(ElementTy, Offset);
+  if (Offset != 0)
+    return nullptr;
+
+  for (const APInt &Index : IntIndices)
+    Indices.push_back(IRB.getInt(Index));
+  return getNaturalGEPWithType(IRB, DL, Ptr, ElementTy, TargetTy, Indices,
+                               NamePrefix);
+}
+
+/// Compute an adjusted pointer from Ptr by Offset bytes where the
+/// resulting pointer has PointerTy.
+///
+/// This tries very hard to compute a "natural" GEP which arrives at the offset
+/// and produces the pointer type desired. Where it cannot, it will try to use
+/// the natural GEP to arrive at the offset and bitcast to the type. Where that
+/// fails, it will try to use an existing i8* and GEP to the byte offset and
+/// bitcast to the type.
+///
+/// The strategy for finding the more natural GEPs is to peel off layers of the
+/// pointer, walking back through bit casts and GEPs, searching for a base
+/// pointer from which we can compute a natural GEP with the desired
+/// properties. The algorithm tries to fold as many constant indices into
+/// a single GEP as possible, thus making each GEP more independent of the
+/// surrounding code.
+static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr,
+                             APInt Offset, Type *PointerTy,
+                             const Twine &NamePrefix) {
+  // Create i8 GEP for opaque pointers.
+  if (Ptr->getType()->isOpaquePointerTy()) {
+    if (Offset != 0)
+      Ptr = IRB.CreateInBoundsGEP(IRB.getInt8Ty(), Ptr, IRB.getInt(Offset),
+                                  NamePrefix + "sroa_idx");
+    return IRB.CreatePointerBitCastOrAddrSpaceCast(Ptr, PointerTy,
+                                                   NamePrefix + "sroa_cast");
+  }
+
+  // Even though we don't look through PHI nodes, we could be called on an
+  // instruction in an unreachable block, which may be on a cycle.
+  SmallPtrSet<Value *, 4> Visited;
+  Visited.insert(Ptr);
+  SmallVector<Value *, 4> Indices;
+
+  // We may end up computing an offset pointer that has the wrong type. If we
+  // never are able to compute one directly that has the correct type, we'll
+  // fall back to it, so keep it and the base it was computed from around here.
+  Value *OffsetPtr = nullptr;
+  Value *OffsetBasePtr;
+
+  // Remember any i8 pointer we come across to re-use if we need to do a raw
+  // byte offset.
+  Value *Int8Ptr = nullptr;
+  APInt Int8PtrOffset(Offset.getBitWidth(), 0);
+
+  PointerType *TargetPtrTy = cast<PointerType>(PointerTy);
+  Type *TargetTy = TargetPtrTy->getNonOpaquePointerElementType();
+
+  // As `addrspacecast` is , `Ptr` (the storage pointer) may have different
+  // address space from the expected `PointerTy` (the pointer to be used).
+  // Adjust the pointer type based the original storage pointer.
+  auto AS = cast<PointerType>(Ptr->getType())->getAddressSpace();
+  PointerTy = TargetTy->getPointerTo(AS);
+
+  do {
+    // First fold any existing GEPs into the offset.
+    while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
+      APInt GEPOffset(Offset.getBitWidth(), 0);
+      if (!GEP->accumulateConstantOffset(DL, GEPOffset))
+        break;
+      Offset += GEPOffset;
+      Ptr = GEP->getPointerOperand();
+      if (!Visited.insert(Ptr).second)
+        break;
+    }
+
+    // See if we can perform a natural GEP here.
+    Indices.clear();
+    if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy,
+                                           Indices, NamePrefix)) {
+      // If we have a new natural pointer at the offset, clear out any old
+      // offset pointer we computed. Unless it is the base pointer or
+      // a non-instruction, we built a GEP we don't need. Zap it.
+      if (OffsetPtr && OffsetPtr != OffsetBasePtr)
+        if (Instruction *I = dyn_cast<Instruction>(OffsetPtr)) {
+          assert(I->use_empty() && "Built a GEP with uses some how!");
+          I->eraseFromParent();
+        }
+      OffsetPtr = P;
+      OffsetBasePtr = Ptr;
+      // If we also found a pointer of the right type, we're done.
+      if (P->getType() == PointerTy)
+        break;
+    }
+
+    // Stash this pointer if we've found an i8*.
+    if (Ptr->getType()->isIntegerTy(8)) {
+      Int8Ptr = Ptr;
+      Int8PtrOffset = Offset;
+    }
+
+    // Peel off a layer of the pointer and update the offset appropriately.
+    if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
+      Ptr = cast<Operator>(Ptr)->getOperand(0);
+    } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
+      if (GA->isInterposable())
+        break;
+      Ptr = GA->getAliasee();
+    } else {
+      break;
+    }
+    assert(Ptr->getType()->isPointerTy() && "Unexpected operand type!");
+  } while (Visited.insert(Ptr).second);
+
+  if (!OffsetPtr) {
+    if (!Int8Ptr) {
+      Int8Ptr = IRB.CreateBitCast(
+          Ptr, IRB.getInt8PtrTy(PointerTy->getPointerAddressSpace()),
+          NamePrefix + "sroa_raw_cast");
+      Int8PtrOffset = Offset;
+    }
+
+    OffsetPtr = Int8PtrOffset == 0
+                    ? Int8Ptr
+                    : IRB.CreateInBoundsGEP(IRB.getInt8Ty(), Int8Ptr,
+                                            IRB.getInt(Int8PtrOffset),
+                                            NamePrefix + "sroa_raw_idx");
+  }
+  Ptr = OffsetPtr;
+
+  // On the off chance we were targeting i8*, guard the bitcast here.
+  if (cast<PointerType>(Ptr->getType()) != TargetPtrTy) {
+    Ptr = IRB.CreatePointerBitCastOrAddrSpaceCast(Ptr,
+                                                  TargetPtrTy,
+                                                  NamePrefix + "sroa_cast");
+  }
+
+  return Ptr;
+}
+
+/// Compute the adjusted alignment for a load or store from an offset.
+static Align getAdjustedAlignment(Instruction *I, uint64_t Offset) {
+  return commonAlignment(getLoadStoreAlignment(I), Offset);
+}
+
+/// Test whether we can convert a value from the old to the new type.
+///
+/// This predicate should be used to guard calls to convertValue in order to
+/// ensure that we only try to convert viable values. The strategy is that we
+/// will peel off single element struct and array wrappings to get to an
+/// underlying value, and convert that value.
+static bool canConvertValue(const DataLayout &DL, Type *OldTy, Type *NewTy) {
+  if (OldTy == NewTy)
+    return true;
+
+  // For integer types, we can't handle any bit-width differences. This would
+  // break both vector conversions with extension and introduce endianness
+  // issues when in conjunction with loads and stores.
+  if (isa<IntegerType>(OldTy) && isa<IntegerType>(NewTy)) {
+    assert(cast<IntegerType>(OldTy)->getBitWidth() !=
+               cast<IntegerType>(NewTy)->getBitWidth() &&
+           "We can't have the same bitwidth for different int types");
+    return false;
+  }
+
+  if (DL.getTypeSizeInBits(NewTy).getFixedValue() !=
+      DL.getTypeSizeInBits(OldTy).getFixedValue())
+    return false;
+  if (!NewTy->isSingleValueType() || !OldTy->isSingleValueType())
+    return false;
+
+  // We can convert pointers to integers and vice-versa. Same for vectors
+  // of pointers and integers.
+  OldTy = OldTy->getScalarType();
+  NewTy = NewTy->getScalarType();
+  if (NewTy->isPointerTy() || OldTy->isPointerTy()) {
+    if (NewTy->isPointerTy() && OldTy->isPointerTy()) {
+      unsigned OldAS = OldTy->getPointerAddressSpace();
+      unsigned NewAS = NewTy->getPointerAddressSpace();
+      // Convert pointers if they are pointers from the same address space or
+      // different integral (not non-integral) address spaces with the same
+      // pointer size.
+      return OldAS == NewAS ||
+             (!DL.isNonIntegralAddressSpace(OldAS) &&
+              !DL.isNonIntegralAddressSpace(NewAS) &&
+              DL.getPointerSize(OldAS) == DL.getPointerSize(NewAS));
+    }
+
+    // We can convert integers to integral pointers, but not to non-integral
+    // pointers.
+    if (OldTy->isIntegerTy())
+      return !DL.isNonIntegralPointerType(NewTy);
+
+    // We can convert integral pointers to integers, but non-integral pointers
+    // need to remain pointers.
+    if (!DL.isNonIntegralPointerType(OldTy))
+      return NewTy->isIntegerTy();
+
+    return false;
+  }
+
+  if (OldTy->isTargetExtTy() || NewTy->isTargetExtTy())
+    return false;
+
+  return true;
+}
+
+/// Generic routine to convert an SSA value to a value of a different
+/// type.
+///
+/// This will try various different casting techniques, such as bitcasts,
+/// inttoptr, and ptrtoint casts. Use the \c canConvertValue predicate to test
+/// two types for viability with this routine.
+static Value *convertValue(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
+                           Type *NewTy) {
+  Type *OldTy = V->getType();
+  assert(canConvertValue(DL, OldTy, NewTy) && "Value not convertable to type");
+
+  if (OldTy == NewTy)
+    return V;
+
+  assert(!(isa<IntegerType>(OldTy) && isa<IntegerType>(NewTy)) &&
+         "Integer types must be the exact same to convert.");
+
+  // See if we need inttoptr for this type pair. May require additional bitcast.
+  if (OldTy->isIntOrIntVectorTy() && NewTy->isPtrOrPtrVectorTy()) {
+    // Expand <2 x i32> to i8* --> <2 x i32> to i64 to i8*
+    // Expand i128 to <2 x i8*> --> i128 to <2 x i64> to <2 x i8*>
+    // Expand <4 x i32> to <2 x i8*> --> <4 x i32> to <2 x i64> to <2 x i8*>
+    // Directly handle i64 to i8*
+    return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
+                              NewTy);
+  }
+
+  // See if we need ptrtoint for this type pair. May require additional bitcast.
+  if (OldTy->isPtrOrPtrVectorTy() && NewTy->isIntOrIntVectorTy()) {
+    // Expand <2 x i8*> to i128 --> <2 x i8*> to <2 x i64> to i128
+    // Expand i8* to <2 x i32> --> i8* to i64 to <2 x i32>
+    // Expand <2 x i8*> to <4 x i32> --> <2 x i8*> to <2 x i64> to <4 x i32>
+    // Expand i8* to i64 --> i8* to i64 to i64
+    return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
+                             NewTy);
+  }
+
+  if (OldTy->isPtrOrPtrVectorTy() && NewTy->isPtrOrPtrVectorTy()) {
+    unsigned OldAS = OldTy->getPointerAddressSpace();
+    unsigned NewAS = NewTy->getPointerAddressSpace();
+    // To convert pointers with different address spaces (they are already
+    // checked convertible, i.e. they have the same pointer size), so far we
+    // cannot use `bitcast` (which has restrict on the same address space) or
+    // `addrspacecast` (which is not always no-op casting). Instead, use a pair
+    // of no-op `ptrtoint`/`inttoptr` casts through an integer with the same bit
+    // size.
+    if (OldAS != NewAS) {
+      assert(DL.getPointerSize(OldAS) == DL.getPointerSize(NewAS));
+      return IRB.CreateIntToPtr(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
+                                NewTy);
+    }
+  }
+
+  return IRB.CreateBitCast(V, NewTy);
+}
+
+/// Test whether the given slice use can be promoted to a vector.
+///
+/// This function is called to test each entry in a partition which is slated
+/// for a single slice.
+static bool isVectorPromotionViableForSlice(Partition &P, const Slice &S,
+                                            VectorType *Ty,
+                                            uint64_t ElementSize,
+                                            const DataLayout &DL) {
+  // First validate the slice offsets.
+  uint64_t BeginOffset =
+      std::max(S.beginOffset(), P.beginOffset()) - P.beginOffset();
+  uint64_t BeginIndex = BeginOffset / ElementSize;
+  if (BeginIndex * ElementSize != BeginOffset ||
+      BeginIndex >= cast<FixedVectorType>(Ty)->getNumElements())
+    return false;
+  uint64_t EndOffset =
+      std::min(S.endOffset(), P.endOffset()) - P.beginOffset();
+  uint64_t EndIndex = EndOffset / ElementSize;
+  if (EndIndex * ElementSize != EndOffset ||
+      EndIndex > cast<FixedVectorType>(Ty)->getNumElements())
+    return false;
+
+  assert(EndIndex > BeginIndex && "Empty vector!");
+  uint64_t NumElements = EndIndex - BeginIndex;
+  Type *SliceTy = (NumElements == 1)
+                      ? Ty->getElementType()
+                      : FixedVectorType::get(Ty->getElementType(), NumElements);
+
+  Type *SplitIntTy =
+      Type::getIntNTy(Ty->getContext(), NumElements * ElementSize * 8);
+
+  Use *U = S.getUse();
+
+  if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
+    if (MI->isVolatile())
+      return false;
+    if (!S.isSplittable())
+      return false; // Skip any unsplittable intrinsics.
+  } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
+    if (!II->isLifetimeStartOrEnd() && !II->isDroppable())
+      return false;
+  } else if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
+    if (LI->isVolatile())
+      return false;
+    Type *LTy = LI->getType();
+    // Disable vector promotion when there are loads or stores of an FCA.
+    if (LTy->isStructTy())
+      return false;
+    if (P.beginOffset() > S.beginOffset() || P.endOffset() < S.endOffset()) {
+      assert(LTy->isIntegerTy());
+      LTy = SplitIntTy;
+    }
+    if (!canConvertValue(DL, SliceTy, LTy))
+      return false;
+  } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
+    if (SI->isVolatile())
+      return false;
+    Type *STy = SI->getValueOperand()->getType();
+    // Disable vector promotion when there are loads or stores of an FCA.
+    if (STy->isStructTy())
+      return false;
+    if (P.beginOffset() > S.beginOffset() || P.endOffset() < S.endOffset()) {
+      assert(STy->isIntegerTy());
+      STy = SplitIntTy;
+    }
+    if (!canConvertValue(DL, STy, SliceTy))
+      return false;
+  } else {
+    return false;
+  }
+
+  return true;
+}
+
+/// Test whether a vector type is viable for promotion.
+///
+/// This implements the necessary checking for \c isVectorPromotionViable over
+/// all slices of the alloca for the given VectorType.
+static bool checkVectorTypeForPromotion(Partition &P, VectorType *VTy,
+                                        const DataLayout &DL) {
+  uint64_t ElementSize =
+      DL.getTypeSizeInBits(VTy->getElementType()).getFixedValue();
+
+  // While the definition of LLVM vectors is bitpacked, we don't support sizes
+  // that aren't byte sized.
+  if (ElementSize % 8)
+    return false;
+  assert((DL.getTypeSizeInBits(VTy).getFixedValue() % 8) == 0 &&
+         "vector size not a multiple of element size?");
+  ElementSize /= 8;
+
+  for (const Slice &S : P)
+    if (!isVectorPromotionViableForSlice(P, S, VTy, ElementSize, DL))
+      return false;
+
+  for (const Slice *S : P.splitSliceTails())
+    if (!isVectorPromotionViableForSlice(P, *S, VTy, ElementSize, DL))
+      return false;
+
+  return true;
+}
+
+/// Test whether the given alloca partitioning and range of slices can be
+/// promoted to a vector.
+///
+/// This is a quick test to check whether we can rewrite a particular alloca
+/// partition (and its newly formed alloca) into a vector alloca with only
+/// whole-vector loads and stores such that it could be promoted to a vector
+/// SSA value. We only can ensure this for a limited set of operations, and we
+/// don't want to do the rewrites unless we are confident that the result will
+/// be promotable, so we have an early test here.
+static VectorType *isVectorPromotionViable(Partition &P, const DataLayout &DL) {
+  // Collect the candidate types for vector-based promotion. Also track whether
+  // we have different element types.
+  SmallVector<VectorType *, 4> CandidateTys;
+  Type *CommonEltTy = nullptr;
+  VectorType *CommonVecPtrTy = nullptr;
+  bool HaveVecPtrTy = false;
+  bool HaveCommonEltTy = true;
+  bool HaveCommonVecPtrTy = true;
+  auto CheckCandidateType = [&](Type *Ty) {
+    if (auto *VTy = dyn_cast<VectorType>(Ty)) {
+      // Return if bitcast to vectors is different for total size in bits.
+      if (!CandidateTys.empty()) {
+        VectorType *V = CandidateTys[0];
+        if (DL.getTypeSizeInBits(VTy).getFixedValue() !=
+            DL.getTypeSizeInBits(V).getFixedValue()) {
+          CandidateTys.clear();
+          return;
+        }
+      }
+      CandidateTys.push_back(VTy);
+      Type *EltTy = VTy->getElementType();
+
+      if (!CommonEltTy)
+        CommonEltTy = EltTy;
+      else if (CommonEltTy != EltTy)
+        HaveCommonEltTy = false;
+
+      if (EltTy->isPointerTy()) {
+        HaveVecPtrTy = true;
+        if (!CommonVecPtrTy)
+          CommonVecPtrTy = VTy;
+        else if (CommonVecPtrTy != VTy)
+          HaveCommonVecPtrTy = false;
+      }
+    }
+  };
+  // Consider any loads or stores that are the exact size of the slice.
+  for (const Slice &S : P)
+    if (S.beginOffset() == P.beginOffset() &&
+        S.endOffset() == P.endOffset()) {
+      if (auto *LI = dyn_cast<LoadInst>(S.getUse()->getUser()))
+        CheckCandidateType(LI->getType());
+      else if (auto *SI = dyn_cast<StoreInst>(S.getUse()->getUser()))
+        CheckCandidateType(SI->getValueOperand()->getType());
+    }
+
+  // If we didn't find a vector type, nothing to do here.
+  if (CandidateTys.empty())
+    return nullptr;
+
+  // Pointer-ness is sticky, if we had a vector-of-pointers candidate type,
+  // then we should choose it, not some other alternative.
+  // But, we can't perform a no-op pointer address space change via bitcast,
+  // so if we didn't have a common pointer element type, bail.
+  if (HaveVecPtrTy && !HaveCommonVecPtrTy)
+    return nullptr;
+
+  // Try to pick the "best" element type out of the choices.
+  if (!HaveCommonEltTy && HaveVecPtrTy) {
+    // If there was a pointer element type, there's really only one choice.
+    CandidateTys.clear();
+    CandidateTys.push_back(CommonVecPtrTy);
+  } else if (!HaveCommonEltTy && !HaveVecPtrTy) {
+    // Integer-ify vector types.
+    for (VectorType *&VTy : CandidateTys) {
+      if (!VTy->getElementType()->isIntegerTy())
+        VTy = cast<VectorType>(VTy->getWithNewType(IntegerType::getIntNTy(
+            VTy->getContext(), VTy->getScalarSizeInBits())));
+    }
+
+    // Rank the remaining candidate vector types. This is easy because we know
+    // they're all integer vectors. We sort by ascending number of elements.
+    auto RankVectorTypes = [&DL](VectorType *RHSTy, VectorType *LHSTy) {
+      (void)DL;
+      assert(DL.getTypeSizeInBits(RHSTy).getFixedValue() ==
+                 DL.getTypeSizeInBits(LHSTy).getFixedValue() &&
+             "Cannot have vector types of different sizes!");
+      assert(RHSTy->getElementType()->isIntegerTy() &&
+             "All non-integer types eliminated!");
+      assert(LHSTy->getElementType()->isIntegerTy() &&
+             "All non-integer types eliminated!");
+      return cast<FixedVectorType>(RHSTy)->getNumElements() <
+             cast<FixedVectorType>(LHSTy)->getNumElements();
+    };
+    llvm::sort(CandidateTys, RankVectorTypes);
+    CandidateTys.erase(
+        std::unique(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes),
+        CandidateTys.end());
+  } else {
+// The only way to have the same element type in every vector type is to
+// have the same vector type. Check that and remove all but one.
+#ifndef NDEBUG
+    for (VectorType *VTy : CandidateTys) {
+      assert(VTy->getElementType() == CommonEltTy &&
+             "Unaccounted for element type!");
+      assert(VTy == CandidateTys[0] &&
+             "Different vector types with the same element type!");
+    }
+#endif
+    CandidateTys.resize(1);
+  }
+
+  // FIXME: hack. Do we have a named constant for this?
+  // SDAG SDNode can't have more than 65535 operands.
+  llvm::erase_if(CandidateTys, [](VectorType *VTy) {
+    return cast<FixedVectorType>(VTy)->getNumElements() >
+           std::numeric_limits<unsigned short>::max();
+  });
+
+  for (VectorType *VTy : CandidateTys)
+    if (checkVectorTypeForPromotion(P, VTy, DL))
+      return VTy;
+
+  return nullptr;
+}
+
+/// Test whether a slice of an alloca is valid for integer widening.
+///
+/// This implements the necessary checking for the \c isIntegerWideningViable
+/// test below on a single slice of the alloca.
+static bool isIntegerWideningViableForSlice(const Slice &S,
+                                            uint64_t AllocBeginOffset,
+                                            Type *AllocaTy,
+                                            const DataLayout &DL,
+                                            bool &WholeAllocaOp) {
+  uint64_t Size = DL.getTypeStoreSize(AllocaTy).getFixedValue();
+
+  uint64_t RelBegin = S.beginOffset() - AllocBeginOffset;
+  uint64_t RelEnd = S.endOffset() - AllocBeginOffset;
+
+  Use *U = S.getUse();
+
+  // Lifetime intrinsics operate over the whole alloca whose sizes are usually
+  // larger than other load/store slices (RelEnd > Size). But lifetime are
+  // always promotable and should not impact other slices' promotability of the
+  // partition.
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
+    if (II->isLifetimeStartOrEnd() || II->isDroppable())
+      return true;
+  }
+
+  // We can't reasonably handle cases where the load or store extends past
+  // the end of the alloca's type and into its padding.
+  if (RelEnd > Size)
+    return false;
+
+  if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
+    if (LI->isVolatile())
+      return false;
+    // We can't handle loads that extend past the allocated memory.
+    if (DL.getTypeStoreSize(LI->getType()).getFixedValue() > Size)
+      return false;
+    // So far, AllocaSliceRewriter does not support widening split slice tails
+    // in rewriteIntegerLoad.
+    if (S.beginOffset() < AllocBeginOffset)
+      return false;
+    // Note that we don't count vector loads or stores as whole-alloca
+    // operations which enable integer widening because we would prefer to use
+    // vector widening instead.
+    if (!isa<VectorType>(LI->getType()) && RelBegin == 0 && RelEnd == Size)
+      WholeAllocaOp = true;
+    if (IntegerType *ITy = dyn_cast<IntegerType>(LI->getType())) {
+      if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy).getFixedValue())
+        return false;
+    } else if (RelBegin != 0 || RelEnd != Size ||
+               !canConvertValue(DL, AllocaTy, LI->getType())) {
+      // Non-integer loads need to be convertible from the alloca type so that
+      // they are promotable.
+      return false;
+    }
+  } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
+    Type *ValueTy = SI->getValueOperand()->getType();
+    if (SI->isVolatile())
+      return false;
+    // We can't handle stores that extend past the allocated memory.
+    if (DL.getTypeStoreSize(ValueTy).getFixedValue() > Size)
+      return false;
+    // So far, AllocaSliceRewriter does not support widening split slice tails
+    // in rewriteIntegerStore.
+    if (S.beginOffset() < AllocBeginOffset)
+      return false;
+    // Note that we don't count vector loads or stores as whole-alloca
+    // operations which enable integer widening because we would prefer to use
+    // vector widening instead.
+    if (!isa<VectorType>(ValueTy) && RelBegin == 0 && RelEnd == Size)
+      WholeAllocaOp = true;
+    if (IntegerType *ITy = dyn_cast<IntegerType>(ValueTy)) {
+      if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy).getFixedValue())
+        return false;
+    } else if (RelBegin != 0 || RelEnd != Size ||
+               !canConvertValue(DL, ValueTy, AllocaTy)) {
+      // Non-integer stores need to be convertible to the alloca type so that
+      // they are promotable.
+      return false;
+    }
+  } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
+    if (MI->isVolatile() || !isa<Constant>(MI->getLength()))
+      return false;
+    if (!S.isSplittable())
+      return false; // Skip any unsplittable intrinsics.
+  } else {
+    return false;
+  }
+
+  return true;
+}
+
+/// Test whether the given alloca partition's integer operations can be
+/// widened to promotable ones.
+///
+/// This is a quick test to check whether we can rewrite the integer loads and
+/// stores to a particular alloca into wider loads and stores and be able to
+/// promote the resulting alloca.
+static bool isIntegerWideningViable(Partition &P, Type *AllocaTy,
+                                    const DataLayout &DL) {
+  uint64_t SizeInBits = DL.getTypeSizeInBits(AllocaTy).getFixedValue();
+  // Don't create integer types larger than the maximum bitwidth.
+  if (SizeInBits > IntegerType::MAX_INT_BITS)
+    return false;
+
+  // Don't try to handle allocas with bit-padding.
+  if (SizeInBits != DL.getTypeStoreSizeInBits(AllocaTy).getFixedValue())
+    return false;
+
+  // We need to ensure that an integer type with the appropriate bitwidth can
+  // be converted to the alloca type, whatever that is. We don't want to force
+  // the alloca itself to have an integer type if there is a more suitable one.
+  Type *IntTy = Type::getIntNTy(AllocaTy->getContext(), SizeInBits);
+  if (!canConvertValue(DL, AllocaTy, IntTy) ||
+      !canConvertValue(DL, IntTy, AllocaTy))
+    return false;
+
+  // While examining uses, we ensure that the alloca has a covering load or
+  // store. We don't want to widen the integer operations only to fail to
+  // promote due to some other unsplittable entry (which we may make splittable
+  // later). However, if there are only splittable uses, go ahead and assume
+  // that we cover the alloca.
+  // FIXME: We shouldn't consider split slices that happen to start in the
+  // partition here...
+  bool WholeAllocaOp = P.empty() && DL.isLegalInteger(SizeInBits);
+
+  for (const Slice &S : P)
+    if (!isIntegerWideningViableForSlice(S, P.beginOffset(), AllocaTy, DL,
+                                         WholeAllocaOp))
+      return false;
+
+  for (const Slice *S : P.splitSliceTails())
+    if (!isIntegerWideningViableForSlice(*S, P.beginOffset(), AllocaTy, DL,
+                                         WholeAllocaOp))
+      return false;
+
+  return WholeAllocaOp;
+}
+
+static Value *extractInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
+                             IntegerType *Ty, uint64_t Offset,
+                             const Twine &Name) {
+  LLVM_DEBUG(dbgs() << "       start: " << *V << "\n");
+  IntegerType *IntTy = cast<IntegerType>(V->getType());
+  assert(DL.getTypeStoreSize(Ty).getFixedValue() + Offset <=
+             DL.getTypeStoreSize(IntTy).getFixedValue() &&
+         "Element extends past full value");
+  uint64_t ShAmt = 8 * Offset;
+  if (DL.isBigEndian())
+    ShAmt = 8 * (DL.getTypeStoreSize(IntTy).getFixedValue() -
+                 DL.getTypeStoreSize(Ty).getFixedValue() - Offset);
+  if (ShAmt) {
+    V = IRB.CreateLShr(V, ShAmt, Name + ".shift");
+    LLVM_DEBUG(dbgs() << "     shifted: " << *V << "\n");
+  }
+  assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
+         "Cannot extract to a larger integer!");
+  if (Ty != IntTy) {
+    V = IRB.CreateTrunc(V, Ty, Name + ".trunc");
+    LLVM_DEBUG(dbgs() << "     trunced: " << *V << "\n");
+  }
+  return V;
+}
+
+static Value *insertInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *Old,
+                            Value *V, uint64_t Offset, const Twine &Name) {
+  IntegerType *IntTy = cast<IntegerType>(Old->getType());
+  IntegerType *Ty = cast<IntegerType>(V->getType());
+  assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
+         "Cannot insert a larger integer!");
+  LLVM_DEBUG(dbgs() << "       start: " << *V << "\n");
+  if (Ty != IntTy) {
+    V = IRB.CreateZExt(V, IntTy, Name + ".ext");
+    LLVM_DEBUG(dbgs() << "    extended: " << *V << "\n");
+  }
+  assert(DL.getTypeStoreSize(Ty).getFixedValue() + Offset <=
+             DL.getTypeStoreSize(IntTy).getFixedValue() &&
+         "Element store outside of alloca store");
+  uint64_t ShAmt = 8 * Offset;
+  if (DL.isBigEndian())
+    ShAmt = 8 * (DL.getTypeStoreSize(IntTy).getFixedValue() -
+                 DL.getTypeStoreSize(Ty).getFixedValue() - Offset);
+  if (ShAmt) {
+    V = IRB.CreateShl(V, ShAmt, Name + ".shift");
+    LLVM_DEBUG(dbgs() << "     shifted: " << *V << "\n");
+  }
+
+  if (ShAmt || Ty->getBitWidth() < IntTy->getBitWidth()) {
+    APInt Mask = ~Ty->getMask().zext(IntTy->getBitWidth()).shl(ShAmt);
+    Old = IRB.CreateAnd(Old, Mask, Name + ".mask");
+    LLVM_DEBUG(dbgs() << "      masked: " << *Old << "\n");
+    V = IRB.CreateOr(Old, V, Name + ".insert");
+    LLVM_DEBUG(dbgs() << "    inserted: " << *V << "\n");
+  }
+  return V;
+}
+
+static Value *extractVector(IRBuilderTy &IRB, Value *V, unsigned BeginIndex,
+                            unsigned EndIndex, const Twine &Name) {
+  auto *VecTy = cast<FixedVectorType>(V->getType());
+  unsigned NumElements = EndIndex - BeginIndex;
+  assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
+
+  if (NumElements == VecTy->getNumElements())
+    return V;
+
+  if (NumElements == 1) {
+    V = IRB.CreateExtractElement(V, IRB.getInt32(BeginIndex),
+                                 Name + ".extract");
+    LLVM_DEBUG(dbgs() << "     extract: " << *V << "\n");
+    return V;
+  }
+
+  auto Mask = llvm::to_vector<8>(llvm::seq<int>(BeginIndex, EndIndex));
+  V = IRB.CreateShuffleVector(V, Mask, Name + ".extract");
+  LLVM_DEBUG(dbgs() << "     shuffle: " << *V << "\n");
+  return V;
+}
+
+static Value *insertVector(IRBuilderTy &IRB, Value *Old, Value *V,
+                           unsigned BeginIndex, const Twine &Name) {
+  VectorType *VecTy = cast<VectorType>(Old->getType());
+  assert(VecTy && "Can only insert a vector into a vector");
+
+  VectorType *Ty = dyn_cast<VectorType>(V->getType());
+  if (!Ty) {
+    // Single element to insert.
+    V = IRB.CreateInsertElement(Old, V, IRB.getInt32(BeginIndex),
+                                Name + ".insert");
+    LLVM_DEBUG(dbgs() << "     insert: " << *V << "\n");
+    return V;
+  }
+
+  assert(cast<FixedVectorType>(Ty)->getNumElements() <=
+             cast<FixedVectorType>(VecTy)->getNumElements() &&
+         "Too many elements!");
+  if (cast<FixedVectorType>(Ty)->getNumElements() ==
+      cast<FixedVectorType>(VecTy)->getNumElements()) {
+    assert(V->getType() == VecTy && "Vector type mismatch");
+    return V;
+  }
+  unsigned EndIndex = BeginIndex + cast<FixedVectorType>(Ty)->getNumElements();
+
+  // When inserting a smaller vector into the larger to store, we first
+  // use a shuffle vector to widen it with undef elements, and then
+  // a second shuffle vector to select between the loaded vector and the
+  // incoming vector.
+  SmallVector<int, 8> Mask;
+  Mask.reserve(cast<FixedVectorType>(VecTy)->getNumElements());
+  for (unsigned i = 0; i != cast<FixedVectorType>(VecTy)->getNumElements(); ++i)
+    if (i >= BeginIndex && i < EndIndex)
+      Mask.push_back(i - BeginIndex);
+    else
+      Mask.push_back(-1);
+  V = IRB.CreateShuffleVector(V, Mask, Name + ".expand");
+  LLVM_DEBUG(dbgs() << "    shuffle: " << *V << "\n");
+
+  SmallVector<Constant *, 8> Mask2;
+  Mask2.reserve(cast<FixedVectorType>(VecTy)->getNumElements());
+  for (unsigned i = 0; i != cast<FixedVectorType>(VecTy)->getNumElements(); ++i)
+    Mask2.push_back(IRB.getInt1(i >= BeginIndex && i < EndIndex));
+
+  V = IRB.CreateSelect(ConstantVector::get(Mask2), V, Old, Name + "blend");
+
+  LLVM_DEBUG(dbgs() << "    blend: " << *V << "\n");
+  return V;
+}
+
+/// Visitor to rewrite instructions using p particular slice of an alloca
+/// to use a new alloca.
+///
+/// Also implements the rewriting to vector-based accesses when the partition
+/// passes the isVectorPromotionViable predicate. Most of the rewriting logic
+/// lives here.
+class llvm::sroa::AllocaSliceRewriter
+    : public InstVisitor<AllocaSliceRewriter, bool> {
+  // Befriend the base class so it can delegate to private visit methods.
+  friend class InstVisitor<AllocaSliceRewriter, bool>;
+
+  using Base = InstVisitor<AllocaSliceRewriter, bool>;
+
+  const DataLayout &DL;
+  AllocaSlices &AS;
+  SROAPass &Pass;
+  AllocaInst &OldAI, &NewAI;
+  const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset;
+  Type *NewAllocaTy;
+
+  // This is a convenience and flag variable that will be null unless the new
+  // alloca's integer operations should be widened to this integer type due to
+  // passing isIntegerWideningViable above. If it is non-null, the desired
+  // integer type will be stored here for easy access during rewriting.
+  IntegerType *IntTy;
+
+  // If we are rewriting an alloca partition which can be written as pure
+  // vector operations, we stash extra information here. When VecTy is
+  // non-null, we have some strict guarantees about the rewritten alloca:
+  //   - The new alloca is exactly the size of the vector type here.
+  //   - The accesses all either map to the entire vector or to a single
+  //     element.
+  //   - The set of accessing instructions is only one of those handled above
+  //     in isVectorPromotionViable. Generally these are the same access kinds
+  //     which are promotable via mem2reg.
+  VectorType *VecTy;
+  Type *ElementTy;
+  uint64_t ElementSize;
+
+  // The original offset of the slice currently being rewritten relative to
+  // the original alloca.
+  uint64_t BeginOffset = 0;
+  uint64_t EndOffset = 0;
+
+  // The new offsets of the slice currently being rewritten relative to the
+  // original alloca.
+  uint64_t NewBeginOffset = 0, NewEndOffset = 0;
+
+  uint64_t RelativeOffset = 0;
+  uint64_t SliceSize = 0;
+  bool IsSplittable = false;
+  bool IsSplit = false;
+  Use *OldUse = nullptr;
+  Instruction *OldPtr = nullptr;
+
+  // Track post-rewrite users which are PHI nodes and Selects.
+  SmallSetVector<PHINode *, 8> &PHIUsers;
+  SmallSetVector<SelectInst *, 8> &SelectUsers;
+
+  // Utility IR builder, whose name prefix is setup for each visited use, and
+  // the insertion point is set to point to the user.
+  IRBuilderTy IRB;
+
+  // Return the new alloca, addrspacecasted if required to avoid changing the
+  // addrspace of a volatile access.
+  Value *getPtrToNewAI(unsigned AddrSpace, bool IsVolatile) {
+    if (!IsVolatile || AddrSpace == NewAI.getType()->getPointerAddressSpace())
+      return &NewAI;
+
+    Type *AccessTy = NewAI.getAllocatedType()->getPointerTo(AddrSpace);
+    return IRB.CreateAddrSpaceCast(&NewAI, AccessTy);
+  }
+
+public:
+  AllocaSliceRewriter(const DataLayout &DL, AllocaSlices &AS, SROAPass &Pass,
+                      AllocaInst &OldAI, AllocaInst &NewAI,
+                      uint64_t NewAllocaBeginOffset,
+                      uint64_t NewAllocaEndOffset, bool IsIntegerPromotable,
+                      VectorType *PromotableVecTy,
+                      SmallSetVector<PHINode *, 8> &PHIUsers,
+                      SmallSetVector<SelectInst *, 8> &SelectUsers)
+      : DL(DL), AS(AS), Pass(Pass), OldAI(OldAI), NewAI(NewAI),
+        NewAllocaBeginOffset(NewAllocaBeginOffset),
+        NewAllocaEndOffset(NewAllocaEndOffset),
+        NewAllocaTy(NewAI.getAllocatedType()),
+        IntTy(
+            IsIntegerPromotable
+                ? Type::getIntNTy(NewAI.getContext(),
+                                  DL.getTypeSizeInBits(NewAI.getAllocatedType())
+                                      .getFixedValue())
+                : nullptr),
+        VecTy(PromotableVecTy),
+        ElementTy(VecTy ? VecTy->getElementType() : nullptr),
+        ElementSize(VecTy ? DL.getTypeSizeInBits(ElementTy).getFixedValue() / 8
+                          : 0),
+        PHIUsers(PHIUsers), SelectUsers(SelectUsers),
+        IRB(NewAI.getContext(), ConstantFolder()) {
+    if (VecTy) {
+      assert((DL.getTypeSizeInBits(ElementTy).getFixedValue() % 8) == 0 &&
+             "Only multiple-of-8 sized vector elements are viable");
+      ++NumVectorized;
+    }
+    assert((!IntTy && !VecTy) || (IntTy && !VecTy) || (!IntTy && VecTy));
+  }
+
+  bool visit(AllocaSlices::const_iterator I) {
+    bool CanSROA = true;
+    BeginOffset = I->beginOffset();
+    EndOffset = I->endOffset();
+    IsSplittable = I->isSplittable();
+    IsSplit =
+        BeginOffset < NewAllocaBeginOffset || EndOffset > NewAllocaEndOffset;
+    LLVM_DEBUG(dbgs() << "  rewriting " << (IsSplit ? "split " : ""));
+    LLVM_DEBUG(AS.printSlice(dbgs(), I, ""));
+    LLVM_DEBUG(dbgs() << "\n");
+
+    // Compute the intersecting offset range.
+    assert(BeginOffset < NewAllocaEndOffset);
+    assert(EndOffset > NewAllocaBeginOffset);
+    NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
+    NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
+
+    RelativeOffset = NewBeginOffset - BeginOffset;
+    SliceSize = NewEndOffset - NewBeginOffset;
+    LLVM_DEBUG(dbgs() << "   Begin:(" << BeginOffset << ", " << EndOffset
+                      << ") NewBegin:(" << NewBeginOffset << ", "
+                      << NewEndOffset << ") NewAllocaBegin:("
+                      << NewAllocaBeginOffset << ", " << NewAllocaEndOffset
+                      << ")\n");
+    assert(IsSplit || RelativeOffset == 0);
+    OldUse = I->getUse();
+    OldPtr = cast<Instruction>(OldUse->get());
+
+    Instruction *OldUserI = cast<Instruction>(OldUse->getUser());
+    IRB.SetInsertPoint(OldUserI);
+    IRB.SetCurrentDebugLocation(OldUserI->getDebugLoc());
+    IRB.getInserter().SetNamePrefix(
+        Twine(NewAI.getName()) + "." + Twine(BeginOffset) + ".");
+
+    CanSROA &= visit(cast<Instruction>(OldUse->getUser()));
+    if (VecTy || IntTy)
+      assert(CanSROA);
+    return CanSROA;
+  }
+
+private:
+  // Make sure the other visit overloads are visible.
+  using Base::visit;
+
+  // Every instruction which can end up as a user must have a rewrite rule.
+  bool visitInstruction(Instruction &I) {
+    LLVM_DEBUG(dbgs() << "    !!!! Cannot rewrite: " << I << "\n");
+    llvm_unreachable("No rewrite rule for this instruction!");
+  }
+
+  Value *getNewAllocaSlicePtr(IRBuilderTy &IRB, Type *PointerTy) {
+    // Note that the offset computation can use BeginOffset or NewBeginOffset
+    // interchangeably for unsplit slices.
+    assert(IsSplit || BeginOffset == NewBeginOffset);
+    uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
+
+#ifndef NDEBUG
+    StringRef OldName = OldPtr->getName();
+    // Skip through the last '.sroa.' component of the name.
+    size_t LastSROAPrefix = OldName.rfind(".sroa.");
+    if (LastSROAPrefix != StringRef::npos) {
+      OldName = OldName.substr(LastSROAPrefix + strlen(".sroa."));
+      // Look for an SROA slice index.
+      size_t IndexEnd = OldName.find_first_not_of("0123456789");
+      if (IndexEnd != StringRef::npos && OldName[IndexEnd] == '.') {
+        // Strip the index and look for the offset.
+        OldName = OldName.substr(IndexEnd + 1);
+        size_t OffsetEnd = OldName.find_first_not_of("0123456789");
+        if (OffsetEnd != StringRef::npos && OldName[OffsetEnd] == '.')
+          // Strip the offset.
+          OldName = OldName.substr(OffsetEnd + 1);
+      }
+    }
+    // Strip any SROA suffixes as well.
+    OldName = OldName.substr(0, OldName.find(".sroa_"));
+#endif
+
+    return getAdjustedPtr(IRB, DL, &NewAI,
+                          APInt(DL.getIndexTypeSizeInBits(PointerTy), Offset),
+                          PointerTy,
+#ifndef NDEBUG
+                          Twine(OldName) + "."
+#else
+                          Twine()
+#endif
+                          );
+  }
+
+  /// Compute suitable alignment to access this slice of the *new*
+  /// alloca.
+  ///
+  /// You can optionally pass a type to this routine and if that type's ABI
+  /// alignment is itself suitable, this will return zero.
+  Align getSliceAlign() {
+    return commonAlignment(NewAI.getAlign(),
+                           NewBeginOffset - NewAllocaBeginOffset);
+  }
+
+  unsigned getIndex(uint64_t Offset) {
+    assert(VecTy && "Can only call getIndex when rewriting a vector");
+    uint64_t RelOffset = Offset - NewAllocaBeginOffset;
+    assert(RelOffset / ElementSize < UINT32_MAX && "Index out of bounds");
+    uint32_t Index = RelOffset / ElementSize;
+    assert(Index * ElementSize == RelOffset);
+    return Index;
+  }
+
+  void deleteIfTriviallyDead(Value *V) {
+    Instruction *I = cast<Instruction>(V);
+    if (isInstructionTriviallyDead(I))
+      Pass.DeadInsts.push_back(I);
+  }
+
+  Value *rewriteVectorizedLoadInst(LoadInst &LI) {
+    unsigned BeginIndex = getIndex(NewBeginOffset);
+    unsigned EndIndex = getIndex(NewEndOffset);
+    assert(EndIndex > BeginIndex && "Empty vector!");
+
+    LoadInst *Load = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                           NewAI.getAlign(), "load");
+
+    Load->copyMetadata(LI, {LLVMContext::MD_mem_parallel_loop_access,
+                            LLVMContext::MD_access_group});
+    return extractVector(IRB, Load, BeginIndex, EndIndex, "vec");
+  }
+
+  Value *rewriteIntegerLoad(LoadInst &LI) {
+    assert(IntTy && "We cannot insert an integer to the alloca");
+    assert(!LI.isVolatile());
+    Value *V = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                     NewAI.getAlign(), "load");
+    V = convertValue(DL, IRB, V, IntTy);
+    assert(NewBeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
+    uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
+    if (Offset > 0 || NewEndOffset < NewAllocaEndOffset) {
+      IntegerType *ExtractTy = Type::getIntNTy(LI.getContext(), SliceSize * 8);
+      V = extractInteger(DL, IRB, V, ExtractTy, Offset, "extract");
+    }
+    // It is possible that the extracted type is not the load type. This
+    // happens if there is a load past the end of the alloca, and as
+    // a consequence the slice is narrower but still a candidate for integer
+    // lowering. To handle this case, we just zero extend the extracted
+    // integer.
+    assert(cast<IntegerType>(LI.getType())->getBitWidth() >= SliceSize * 8 &&
+           "Can only handle an extract for an overly wide load");
+    if (cast<IntegerType>(LI.getType())->getBitWidth() > SliceSize * 8)
+      V = IRB.CreateZExt(V, LI.getType());
+    return V;
+  }
+
+  bool visitLoadInst(LoadInst &LI) {
+    LLVM_DEBUG(dbgs() << "    original: " << LI << "\n");
+    Value *OldOp = LI.getOperand(0);
+    assert(OldOp == OldPtr);
+
+    AAMDNodes AATags = LI.getAAMetadata();
+
+    unsigned AS = LI.getPointerAddressSpace();
+
+    Type *TargetTy = IsSplit ? Type::getIntNTy(LI.getContext(), SliceSize * 8)
+                             : LI.getType();
+    const bool IsLoadPastEnd =
+        DL.getTypeStoreSize(TargetTy).getFixedValue() > SliceSize;
+    bool IsPtrAdjusted = false;
+    Value *V;
+    if (VecTy) {
+      V = rewriteVectorizedLoadInst(LI);
+    } else if (IntTy && LI.getType()->isIntegerTy()) {
+      V = rewriteIntegerLoad(LI);
+    } else if (NewBeginOffset == NewAllocaBeginOffset &&
+               NewEndOffset == NewAllocaEndOffset &&
+               (canConvertValue(DL, NewAllocaTy, TargetTy) ||
+                (IsLoadPastEnd && NewAllocaTy->isIntegerTy() &&
+                 TargetTy->isIntegerTy()))) {
+      Value *NewPtr =
+          getPtrToNewAI(LI.getPointerAddressSpace(), LI.isVolatile());
+      LoadInst *NewLI = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), NewPtr,
+                                              NewAI.getAlign(), LI.isVolatile(),
+                                              LI.getName());
+      if (LI.isVolatile())
+        NewLI->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
+      if (NewLI->isAtomic())
+        NewLI->setAlignment(LI.getAlign());
+
+      // Copy any metadata that is valid for the new load. This may require
+      // conversion to a different kind of metadata, e.g. !nonnull might change
+      // to !range or vice versa.
+      copyMetadataForLoad(*NewLI, LI);
+
+      // Do this after copyMetadataForLoad() to preserve the TBAA shift.
+      if (AATags)
+        NewLI->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+
+      // Try to preserve nonnull metadata
+      V = NewLI;
+
+      // If this is an integer load past the end of the slice (which means the
+      // bytes outside the slice are undef or this load is dead) just forcibly
+      // fix the integer size with correct handling of endianness.
+      if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
+        if (auto *TITy = dyn_cast<IntegerType>(TargetTy))
+          if (AITy->getBitWidth() < TITy->getBitWidth()) {
+            V = IRB.CreateZExt(V, TITy, "load.ext");
+            if (DL.isBigEndian())
+              V = IRB.CreateShl(V, TITy->getBitWidth() - AITy->getBitWidth(),
+                                "endian_shift");
+          }
+    } else {
+      Type *LTy = TargetTy->getPointerTo(AS);
+      LoadInst *NewLI =
+          IRB.CreateAlignedLoad(TargetTy, getNewAllocaSlicePtr(IRB, LTy),
+                                getSliceAlign(), LI.isVolatile(), LI.getName());
+      if (AATags)
+        NewLI->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+      if (LI.isVolatile())
+        NewLI->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
+      NewLI->copyMetadata(LI, {LLVMContext::MD_mem_parallel_loop_access,
+                               LLVMContext::MD_access_group});
+
+      V = NewLI;
+      IsPtrAdjusted = true;
+    }
+    V = convertValue(DL, IRB, V, TargetTy);
+
+    if (IsSplit) {
+      assert(!LI.isVolatile());
+      assert(LI.getType()->isIntegerTy() &&
+             "Only integer type loads and stores are split");
+      assert(SliceSize < DL.getTypeStoreSize(LI.getType()).getFixedValue() &&
+             "Split load isn't smaller than original load");
+      assert(DL.typeSizeEqualsStoreSize(LI.getType()) &&
+             "Non-byte-multiple bit width");
+      // Move the insertion point just past the load so that we can refer to it.
+      IRB.SetInsertPoint(&*std::next(BasicBlock::iterator(&LI)));
+      // Create a placeholder value with the same type as LI to use as the
+      // basis for the new value. This allows us to replace the uses of LI with
+      // the computed value, and then replace the placeholder with LI, leaving
+      // LI only used for this computation.
+      Value *Placeholder = new LoadInst(
+          LI.getType(), PoisonValue::get(LI.getType()->getPointerTo(AS)), "",
+          false, Align(1));
+      V = insertInteger(DL, IRB, Placeholder, V, NewBeginOffset - BeginOffset,
+                        "insert");
+      LI.replaceAllUsesWith(V);
+      Placeholder->replaceAllUsesWith(&LI);
+      Placeholder->deleteValue();
+    } else {
+      LI.replaceAllUsesWith(V);
+    }
+
+    Pass.DeadInsts.push_back(&LI);
+    deleteIfTriviallyDead(OldOp);
+    LLVM_DEBUG(dbgs() << "          to: " << *V << "\n");
+    return !LI.isVolatile() && !IsPtrAdjusted;
+  }
+
+  bool rewriteVectorizedStoreInst(Value *V, StoreInst &SI, Value *OldOp,
+                                  AAMDNodes AATags) {
+    // Capture V for the purpose of debug-info accounting once it's converted
+    // to a vector store.
+    Value *OrigV = V;
+    if (V->getType() != VecTy) {
+      unsigned BeginIndex = getIndex(NewBeginOffset);
+      unsigned EndIndex = getIndex(NewEndOffset);
+      assert(EndIndex > BeginIndex && "Empty vector!");
+      unsigned NumElements = EndIndex - BeginIndex;
+      assert(NumElements <= cast<FixedVectorType>(VecTy)->getNumElements() &&
+             "Too many elements!");
+      Type *SliceTy = (NumElements == 1)
+                          ? ElementTy
+                          : FixedVectorType::get(ElementTy, NumElements);
+      if (V->getType() != SliceTy)
+        V = convertValue(DL, IRB, V, SliceTy);
+
+      // Mix in the existing elements.
+      Value *Old = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                         NewAI.getAlign(), "load");
+      V = insertVector(IRB, Old, V, BeginIndex, "vec");
+    }
+    StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlign());
+    Store->copyMetadata(SI, {LLVMContext::MD_mem_parallel_loop_access,
+                             LLVMContext::MD_access_group});
+    if (AATags)
+      Store->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+    Pass.DeadInsts.push_back(&SI);
+
+    // NOTE: Careful to use OrigV rather than V.
+    migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &SI, Store,
+                     Store->getPointerOperand(), OrigV, DL);
+    LLVM_DEBUG(dbgs() << "          to: " << *Store << "\n");
+    return true;
+  }
+
+  bool rewriteIntegerStore(Value *V, StoreInst &SI, AAMDNodes AATags) {
+    assert(IntTy && "We cannot extract an integer from the alloca");
+    assert(!SI.isVolatile());
+    if (DL.getTypeSizeInBits(V->getType()).getFixedValue() !=
+        IntTy->getBitWidth()) {
+      Value *Old = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                         NewAI.getAlign(), "oldload");
+      Old = convertValue(DL, IRB, Old, IntTy);
+      assert(BeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
+      uint64_t Offset = BeginOffset - NewAllocaBeginOffset;
+      V = insertInteger(DL, IRB, Old, SI.getValueOperand(), Offset, "insert");
+    }
+    V = convertValue(DL, IRB, V, NewAllocaTy);
+    StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlign());
+    Store->copyMetadata(SI, {LLVMContext::MD_mem_parallel_loop_access,
+                             LLVMContext::MD_access_group});
+    if (AATags)
+      Store->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+
+    migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &SI, Store,
+                     Store->getPointerOperand(), Store->getValueOperand(), DL);
+
+    Pass.DeadInsts.push_back(&SI);
+    LLVM_DEBUG(dbgs() << "          to: " << *Store << "\n");
+    return true;
+  }
+
+  bool visitStoreInst(StoreInst &SI) {
+    LLVM_DEBUG(dbgs() << "    original: " << SI << "\n");
+    Value *OldOp = SI.getOperand(1);
+    assert(OldOp == OldPtr);
+
+    AAMDNodes AATags = SI.getAAMetadata();
+    Value *V = SI.getValueOperand();
+
+    // Strip all inbounds GEPs and pointer casts to try to dig out any root
+    // alloca that should be re-examined after promoting this alloca.
+    if (V->getType()->isPointerTy())
+      if (AllocaInst *AI = dyn_cast<AllocaInst>(V->stripInBoundsOffsets()))
+        Pass.PostPromotionWorklist.insert(AI);
+
+    if (SliceSize < DL.getTypeStoreSize(V->getType()).getFixedValue()) {
+      assert(!SI.isVolatile());
+      assert(V->getType()->isIntegerTy() &&
+             "Only integer type loads and stores are split");
+      assert(DL.typeSizeEqualsStoreSize(V->getType()) &&
+             "Non-byte-multiple bit width");
+      IntegerType *NarrowTy = Type::getIntNTy(SI.getContext(), SliceSize * 8);
+      V = extractInteger(DL, IRB, V, NarrowTy, NewBeginOffset - BeginOffset,
+                         "extract");
+    }
+
+    if (VecTy)
+      return rewriteVectorizedStoreInst(V, SI, OldOp, AATags);
+    if (IntTy && V->getType()->isIntegerTy())
+      return rewriteIntegerStore(V, SI, AATags);
+
+    const bool IsStorePastEnd =
+        DL.getTypeStoreSize(V->getType()).getFixedValue() > SliceSize;
+    StoreInst *NewSI;
+    if (NewBeginOffset == NewAllocaBeginOffset &&
+        NewEndOffset == NewAllocaEndOffset &&
+        (canConvertValue(DL, V->getType(), NewAllocaTy) ||
+         (IsStorePastEnd && NewAllocaTy->isIntegerTy() &&
+          V->getType()->isIntegerTy()))) {
+      // If this is an integer store past the end of slice (and thus the bytes
+      // past that point are irrelevant or this is unreachable), truncate the
+      // value prior to storing.
+      if (auto *VITy = dyn_cast<IntegerType>(V->getType()))
+        if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
+          if (VITy->getBitWidth() > AITy->getBitWidth()) {
+            if (DL.isBigEndian())
+              V = IRB.CreateLShr(V, VITy->getBitWidth() - AITy->getBitWidth(),
+                                 "endian_shift");
+            V = IRB.CreateTrunc(V, AITy, "load.trunc");
+          }
+
+      V = convertValue(DL, IRB, V, NewAllocaTy);
+      Value *NewPtr =
+          getPtrToNewAI(SI.getPointerAddressSpace(), SI.isVolatile());
+
+      NewSI =
+          IRB.CreateAlignedStore(V, NewPtr, NewAI.getAlign(), SI.isVolatile());
+    } else {
+      unsigned AS = SI.getPointerAddressSpace();
+      Value *NewPtr = getNewAllocaSlicePtr(IRB, V->getType()->getPointerTo(AS));
+      NewSI =
+          IRB.CreateAlignedStore(V, NewPtr, getSliceAlign(), SI.isVolatile());
+    }
+    NewSI->copyMetadata(SI, {LLVMContext::MD_mem_parallel_loop_access,
+                             LLVMContext::MD_access_group});
+    if (AATags)
+      NewSI->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+    if (SI.isVolatile())
+      NewSI->setAtomic(SI.getOrdering(), SI.getSyncScopeID());
+    if (NewSI->isAtomic())
+      NewSI->setAlignment(SI.getAlign());
+
+    migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &SI, NewSI,
+                     NewSI->getPointerOperand(), NewSI->getValueOperand(), DL);
+
+    Pass.DeadInsts.push_back(&SI);
+    deleteIfTriviallyDead(OldOp);
+
+    LLVM_DEBUG(dbgs() << "          to: " << *NewSI << "\n");
+    return NewSI->getPointerOperand() == &NewAI &&
+           NewSI->getValueOperand()->getType() == NewAllocaTy &&
+           !SI.isVolatile();
+  }
+
+  /// Compute an integer value from splatting an i8 across the given
+  /// number of bytes.
+  ///
+  /// Note that this routine assumes an i8 is a byte. If that isn't true, don't
+  /// call this routine.
+  /// FIXME: Heed the advice above.
+  ///
+  /// \param V The i8 value to splat.
+  /// \param Size The number of bytes in the output (assuming i8 is one byte)
+  Value *getIntegerSplat(Value *V, unsigned Size) {
+    assert(Size > 0 && "Expected a positive number of bytes.");
+    IntegerType *VTy = cast<IntegerType>(V->getType());
+    assert(VTy->getBitWidth() == 8 && "Expected an i8 value for the byte");
+    if (Size == 1)
+      return V;
+
+    Type *SplatIntTy = Type::getIntNTy(VTy->getContext(), Size * 8);
+    V = IRB.CreateMul(
+        IRB.CreateZExt(V, SplatIntTy, "zext"),
+        IRB.CreateUDiv(Constant::getAllOnesValue(SplatIntTy),
+                       IRB.CreateZExt(Constant::getAllOnesValue(V->getType()),
+                                      SplatIntTy)),
+        "isplat");
+    return V;
+  }
+
+  /// Compute a vector splat for a given element value.
+  Value *getVectorSplat(Value *V, unsigned NumElements) {
+    V = IRB.CreateVectorSplat(NumElements, V, "vsplat");
+    LLVM_DEBUG(dbgs() << "       splat: " << *V << "\n");
+    return V;
+  }
+
+  bool visitMemSetInst(MemSetInst &II) {
+    LLVM_DEBUG(dbgs() << "    original: " << II << "\n");
+    assert(II.getRawDest() == OldPtr);
+
+    AAMDNodes AATags = II.getAAMetadata();
+
+    // If the memset has a variable size, it cannot be split, just adjust the
+    // pointer to the new alloca.
+    if (!isa<ConstantInt>(II.getLength())) {
+      assert(!IsSplit);
+      assert(NewBeginOffset == BeginOffset);
+      II.setDest(getNewAllocaSlicePtr(IRB, OldPtr->getType()));
+      II.setDestAlignment(getSliceAlign());
+      // In theory we should call migrateDebugInfo here. However, we do not
+      // emit dbg.assign intrinsics for mem intrinsics storing through non-
+      // constant geps, or storing a variable number of bytes.
+      assert(at::getAssignmentMarkers(&II).empty() &&
+             "AT: Unexpected link to non-const GEP");
+      deleteIfTriviallyDead(OldPtr);
+      return false;
+    }
+
+    // Record this instruction for deletion.
+    Pass.DeadInsts.push_back(&II);
+
+    Type *AllocaTy = NewAI.getAllocatedType();
+    Type *ScalarTy = AllocaTy->getScalarType();
+
+    const bool CanContinue = [&]() {
+      if (VecTy || IntTy)
+        return true;
+      if (BeginOffset > NewAllocaBeginOffset ||
+          EndOffset < NewAllocaEndOffset)
+        return false;
+      // Length must be in range for FixedVectorType.
+      auto *C = cast<ConstantInt>(II.getLength());
+      const uint64_t Len = C->getLimitedValue();
+      if (Len > std::numeric_limits<unsigned>::max())
+        return false;
+      auto *Int8Ty = IntegerType::getInt8Ty(NewAI.getContext());
+      auto *SrcTy = FixedVectorType::get(Int8Ty, Len);
+      return canConvertValue(DL, SrcTy, AllocaTy) &&
+             DL.isLegalInteger(DL.getTypeSizeInBits(ScalarTy).getFixedValue());
+    }();
+
+    // If this doesn't map cleanly onto the alloca type, and that type isn't
+    // a single value type, just emit a memset.
+    if (!CanContinue) {
+      Type *SizeTy = II.getLength()->getType();
+      Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
+      MemIntrinsic *New = cast<MemIntrinsic>(IRB.CreateMemSet(
+          getNewAllocaSlicePtr(IRB, OldPtr->getType()), II.getValue(), Size,
+          MaybeAlign(getSliceAlign()), II.isVolatile()));
+      if (AATags)
+        New->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+
+      migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &II, New,
+                       New->getRawDest(), nullptr, DL);
+
+      LLVM_DEBUG(dbgs() << "          to: " << *New << "\n");
+      return false;
+    }
+
+    // If we can represent this as a simple value, we have to build the actual
+    // value to store, which requires expanding the byte present in memset to
+    // a sensible representation for the alloca type. This is essentially
+    // splatting the byte to a sufficiently wide integer, splatting it across
+    // any desired vector width, and bitcasting to the final type.
+    Value *V;
+
+    if (VecTy) {
+      // If this is a memset of a vectorized alloca, insert it.
+      assert(ElementTy == ScalarTy);
+
+      unsigned BeginIndex = getIndex(NewBeginOffset);
+      unsigned EndIndex = getIndex(NewEndOffset);
+      assert(EndIndex > BeginIndex && "Empty vector!");
+      unsigned NumElements = EndIndex - BeginIndex;
+      assert(NumElements <= cast<FixedVectorType>(VecTy)->getNumElements() &&
+             "Too many elements!");
+
+      Value *Splat = getIntegerSplat(
+          II.getValue(), DL.getTypeSizeInBits(ElementTy).getFixedValue() / 8);
+      Splat = convertValue(DL, IRB, Splat, ElementTy);
+      if (NumElements > 1)
+        Splat = getVectorSplat(Splat, NumElements);
+
+      Value *Old = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                         NewAI.getAlign(), "oldload");
+      V = insertVector(IRB, Old, Splat, BeginIndex, "vec");
+    } else if (IntTy) {
+      // If this is a memset on an alloca where we can widen stores, insert the
+      // set integer.
+      assert(!II.isVolatile());
+
+      uint64_t Size = NewEndOffset - NewBeginOffset;
+      V = getIntegerSplat(II.getValue(), Size);
+
+      if (IntTy && (BeginOffset != NewAllocaBeginOffset ||
+                    EndOffset != NewAllocaBeginOffset)) {
+        Value *Old = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                           NewAI.getAlign(), "oldload");
+        Old = convertValue(DL, IRB, Old, IntTy);
+        uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
+        V = insertInteger(DL, IRB, Old, V, Offset, "insert");
+      } else {
+        assert(V->getType() == IntTy &&
+               "Wrong type for an alloca wide integer!");
+      }
+      V = convertValue(DL, IRB, V, AllocaTy);
+    } else {
+      // Established these invariants above.
+      assert(NewBeginOffset == NewAllocaBeginOffset);
+      assert(NewEndOffset == NewAllocaEndOffset);
+
+      V = getIntegerSplat(II.getValue(),
+                          DL.getTypeSizeInBits(ScalarTy).getFixedValue() / 8);
+      if (VectorType *AllocaVecTy = dyn_cast<VectorType>(AllocaTy))
+        V = getVectorSplat(
+            V, cast<FixedVectorType>(AllocaVecTy)->getNumElements());
+
+      V = convertValue(DL, IRB, V, AllocaTy);
+    }
+
+    Value *NewPtr = getPtrToNewAI(II.getDestAddressSpace(), II.isVolatile());
+    StoreInst *New =
+        IRB.CreateAlignedStore(V, NewPtr, NewAI.getAlign(), II.isVolatile());
+    New->copyMetadata(II, {LLVMContext::MD_mem_parallel_loop_access,
+                           LLVMContext::MD_access_group});
+    if (AATags)
+      New->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+
+    migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &II, New,
+                     New->getPointerOperand(), V, DL);
+
+    LLVM_DEBUG(dbgs() << "          to: " << *New << "\n");
+    return !II.isVolatile();
+  }
+
+  bool visitMemTransferInst(MemTransferInst &II) {
+    // Rewriting of memory transfer instructions can be a bit tricky. We break
+    // them into two categories: split intrinsics and unsplit intrinsics.
+
+    LLVM_DEBUG(dbgs() << "    original: " << II << "\n");
+
+    AAMDNodes AATags = II.getAAMetadata();
+
+    bool IsDest = &II.getRawDestUse() == OldUse;
+    assert((IsDest && II.getRawDest() == OldPtr) ||
+           (!IsDest && II.getRawSource() == OldPtr));
+
+    Align SliceAlign = getSliceAlign();
+    // For unsplit intrinsics, we simply modify the source and destination
+    // pointers in place. This isn't just an optimization, it is a matter of
+    // correctness. With unsplit intrinsics we may be dealing with transfers
+    // within a single alloca before SROA ran, or with transfers that have
+    // a variable length. We may also be dealing with memmove instead of
+    // memcpy, and so simply updating the pointers is the necessary for us to
+    // update both source and dest of a single call.
+    if (!IsSplittable) {
+      Value *AdjustedPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
+      if (IsDest) {
+        // Update the address component of linked dbg.assigns.
+        for (auto *DAI : at::getAssignmentMarkers(&II)) {
+          if (any_of(DAI->location_ops(),
+                     [&](Value *V) { return V == II.getDest(); }) ||
+              DAI->getAddress() == II.getDest())
+            DAI->replaceVariableLocationOp(II.getDest(), AdjustedPtr);
+        }
+        II.setDest(AdjustedPtr);
+        II.setDestAlignment(SliceAlign);
+      } else {
+        II.setSource(AdjustedPtr);
+        II.setSourceAlignment(SliceAlign);
+      }
+
+      LLVM_DEBUG(dbgs() << "          to: " << II << "\n");
+      deleteIfTriviallyDead(OldPtr);
+      return false;
+    }
+    // For split transfer intrinsics we have an incredibly useful assurance:
+    // the source and destination do not reside within the same alloca, and at
+    // least one of them does not escape. This means that we can replace
+    // memmove with memcpy, and we don't need to worry about all manner of
+    // downsides to splitting and transforming the operations.
+
+    // If this doesn't map cleanly onto the alloca type, and that type isn't
+    // a single value type, just emit a memcpy.
+    bool EmitMemCpy =
+        !VecTy && !IntTy &&
+        (BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset ||
+         SliceSize !=
+             DL.getTypeStoreSize(NewAI.getAllocatedType()).getFixedValue() ||
+         !NewAI.getAllocatedType()->isSingleValueType());
+
+    // If we're just going to emit a memcpy, the alloca hasn't changed, and the
+    // size hasn't been shrunk based on analysis of the viable range, this is
+    // a no-op.
+    if (EmitMemCpy && &OldAI == &NewAI) {
+      // Ensure the start lines up.
+      assert(NewBeginOffset == BeginOffset);
+
+      // Rewrite the size as needed.
+      if (NewEndOffset != EndOffset)
+        II.setLength(ConstantInt::get(II.getLength()->getType(),
+                                      NewEndOffset - NewBeginOffset));
+      return false;
+    }
+    // Record this instruction for deletion.
+    Pass.DeadInsts.push_back(&II);
+
+    // Strip all inbounds GEPs and pointer casts to try to dig out any root
+    // alloca that should be re-examined after rewriting this instruction.
+    Value *OtherPtr = IsDest ? II.getRawSource() : II.getRawDest();
+    if (AllocaInst *AI =
+            dyn_cast<AllocaInst>(OtherPtr->stripInBoundsOffsets())) {
+      assert(AI != &OldAI && AI != &NewAI &&
+             "Splittable transfers cannot reach the same alloca on both ends.");
+      Pass.Worklist.insert(AI);
+    }
+
+    Type *OtherPtrTy = OtherPtr->getType();
+    unsigned OtherAS = OtherPtrTy->getPointerAddressSpace();
+
+    // Compute the relative offset for the other pointer within the transfer.
+    unsigned OffsetWidth = DL.getIndexSizeInBits(OtherAS);
+    APInt OtherOffset(OffsetWidth, NewBeginOffset - BeginOffset);
+    Align OtherAlign =
+        (IsDest ? II.getSourceAlign() : II.getDestAlign()).valueOrOne();
+    OtherAlign =
+        commonAlignment(OtherAlign, OtherOffset.zextOrTrunc(64).getZExtValue());
+
+    if (EmitMemCpy) {
+      // Compute the other pointer, folding as much as possible to produce
+      // a single, simple GEP in most cases.
+      OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
+                                OtherPtr->getName() + ".");
+
+      Value *OurPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
+      Type *SizeTy = II.getLength()->getType();
+      Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
+
+      Value *DestPtr, *SrcPtr;
+      MaybeAlign DestAlign, SrcAlign;
+      // Note: IsDest is true iff we're copying into the new alloca slice
+      if (IsDest) {
+        DestPtr = OurPtr;
+        DestAlign = SliceAlign;
+        SrcPtr = OtherPtr;
+        SrcAlign = OtherAlign;
+      } else {
+        DestPtr = OtherPtr;
+        DestAlign = OtherAlign;
+        SrcPtr = OurPtr;
+        SrcAlign = SliceAlign;
+      }
+      CallInst *New = IRB.CreateMemCpy(DestPtr, DestAlign, SrcPtr, SrcAlign,
+                                       Size, II.isVolatile());
+      if (AATags)
+        New->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+
+      migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &II, New,
+                       DestPtr, nullptr, DL);
+      LLVM_DEBUG(dbgs() << "          to: " << *New << "\n");
+      return false;
+    }
+
+    bool IsWholeAlloca = NewBeginOffset == NewAllocaBeginOffset &&
+                         NewEndOffset == NewAllocaEndOffset;
+    uint64_t Size = NewEndOffset - NewBeginOffset;
+    unsigned BeginIndex = VecTy ? getIndex(NewBeginOffset) : 0;
+    unsigned EndIndex = VecTy ? getIndex(NewEndOffset) : 0;
+    unsigned NumElements = EndIndex - BeginIndex;
+    IntegerType *SubIntTy =
+        IntTy ? Type::getIntNTy(IntTy->getContext(), Size * 8) : nullptr;
+
+    // Reset the other pointer type to match the register type we're going to
+    // use, but using the address space of the original other pointer.
+    Type *OtherTy;
+    if (VecTy && !IsWholeAlloca) {
+      if (NumElements == 1)
+        OtherTy = VecTy->getElementType();
+      else
+        OtherTy = FixedVectorType::get(VecTy->getElementType(), NumElements);
+    } else if (IntTy && !IsWholeAlloca) {
+      OtherTy = SubIntTy;
+    } else {
+      OtherTy = NewAllocaTy;
+    }
+    OtherPtrTy = OtherTy->getPointerTo(OtherAS);
+
+    Value *AdjPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
+                                   OtherPtr->getName() + ".");
+    MaybeAlign SrcAlign = OtherAlign;
+    MaybeAlign DstAlign = SliceAlign;
+    if (!IsDest)
+      std::swap(SrcAlign, DstAlign);
+
+    Value *SrcPtr;
+    Value *DstPtr;
+
+    if (IsDest) {
+      DstPtr = getPtrToNewAI(II.getDestAddressSpace(), II.isVolatile());
+      SrcPtr = AdjPtr;
+    } else {
+      DstPtr = AdjPtr;
+      SrcPtr = getPtrToNewAI(II.getSourceAddressSpace(), II.isVolatile());
+    }
+
+    Value *Src;
+    if (VecTy && !IsWholeAlloca && !IsDest) {
+      Src = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                  NewAI.getAlign(), "load");
+      Src = extractVector(IRB, Src, BeginIndex, EndIndex, "vec");
+    } else if (IntTy && !IsWholeAlloca && !IsDest) {
+      Src = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                  NewAI.getAlign(), "load");
+      Src = convertValue(DL, IRB, Src, IntTy);
+      uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
+      Src = extractInteger(DL, IRB, Src, SubIntTy, Offset, "extract");
+    } else {
+      LoadInst *Load = IRB.CreateAlignedLoad(OtherTy, SrcPtr, SrcAlign,
+                                             II.isVolatile(), "copyload");
+      Load->copyMetadata(II, {LLVMContext::MD_mem_parallel_loop_access,
+                              LLVMContext::MD_access_group});
+      if (AATags)
+        Load->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+      Src = Load;
+    }
+
+    if (VecTy && !IsWholeAlloca && IsDest) {
+      Value *Old = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                         NewAI.getAlign(), "oldload");
+      Src = insertVector(IRB, Old, Src, BeginIndex, "vec");
+    } else if (IntTy && !IsWholeAlloca && IsDest) {
+      Value *Old = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), &NewAI,
+                                         NewAI.getAlign(), "oldload");
+      Old = convertValue(DL, IRB, Old, IntTy);
+      uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
+      Src = insertInteger(DL, IRB, Old, Src, Offset, "insert");
+      Src = convertValue(DL, IRB, Src, NewAllocaTy);
+    }
+
+    StoreInst *Store = cast<StoreInst>(
+        IRB.CreateAlignedStore(Src, DstPtr, DstAlign, II.isVolatile()));
+    Store->copyMetadata(II, {LLVMContext::MD_mem_parallel_loop_access,
+                             LLVMContext::MD_access_group});
+    if (AATags)
+      Store->setAAMetadata(AATags.shift(NewBeginOffset - BeginOffset));
+
+    migrateDebugInfo(&OldAI, RelativeOffset * 8, SliceSize * 8, &II, Store,
+                     DstPtr, Src, DL);
+    LLVM_DEBUG(dbgs() << "          to: " << *Store << "\n");
+    return !II.isVolatile();
+  }
+
+  bool visitIntrinsicInst(IntrinsicInst &II) {
+    assert((II.isLifetimeStartOrEnd() || II.isDroppable()) &&
+           "Unexpected intrinsic!");
+    LLVM_DEBUG(dbgs() << "    original: " << II << "\n");
+
+    // Record this instruction for deletion.
+    Pass.DeadInsts.push_back(&II);
+
+    if (II.isDroppable()) {
+      assert(II.getIntrinsicID() == Intrinsic::assume && "Expected assume");
+      // TODO For now we forget assumed information, this can be improved.
+      OldPtr->dropDroppableUsesIn(II);
+      return true;
+    }
+
+    assert(II.getArgOperand(1) == OldPtr);
+    // Lifetime intrinsics are only promotable if they cover the whole alloca.
+    // Therefore, we drop lifetime intrinsics which don't cover the whole
+    // alloca.
+    // (In theory, intrinsics which partially cover an alloca could be
+    // promoted, but PromoteMemToReg doesn't handle that case.)
+    // FIXME: Check whether the alloca is promotable before dropping the
+    // lifetime intrinsics?
+    if (NewBeginOffset != NewAllocaBeginOffset ||
+        NewEndOffset != NewAllocaEndOffset)
+      return true;
+
+    ConstantInt *Size =
+        ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()),
+                         NewEndOffset - NewBeginOffset);
+    // Lifetime intrinsics always expect an i8* so directly get such a pointer
+    // for the new alloca slice.
+    Type *PointerTy = IRB.getInt8PtrTy(OldPtr->getType()->getPointerAddressSpace());
+    Value *Ptr = getNewAllocaSlicePtr(IRB, PointerTy);
+    Value *New;
+    if (II.getIntrinsicID() == Intrinsic::lifetime_start)
+      New = IRB.CreateLifetimeStart(Ptr, Size);
+    else
+      New = IRB.CreateLifetimeEnd(Ptr, Size);
+
+    (void)New;
+    LLVM_DEBUG(dbgs() << "          to: " << *New << "\n");
+
+    return true;
+  }
+
+  void fixLoadStoreAlign(Instruction &Root) {
+    // This algorithm implements the same visitor loop as
+    // hasUnsafePHIOrSelectUse, and fixes the alignment of each load
+    // or store found.
+    SmallPtrSet<Instruction *, 4> Visited;
+    SmallVector<Instruction *, 4> Uses;
+    Visited.insert(&Root);
+    Uses.push_back(&Root);
+    do {
+      Instruction *I = Uses.pop_back_val();
+
+      if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+        LI->setAlignment(std::min(LI->getAlign(), getSliceAlign()));
+        continue;
+      }
+      if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+        SI->setAlignment(std::min(SI->getAlign(), getSliceAlign()));
+        continue;
+      }
+
+      assert(isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I) ||
+             isa<PHINode>(I) || isa<SelectInst>(I) ||
+             isa<GetElementPtrInst>(I));
+      for (User *U : I->users())
+        if (Visited.insert(cast<Instruction>(U)).second)
+          Uses.push_back(cast<Instruction>(U));
+    } while (!Uses.empty());
+  }
+
+  bool visitPHINode(PHINode &PN) {
+    LLVM_DEBUG(dbgs() << "    original: " << PN << "\n");
+    assert(BeginOffset >= NewAllocaBeginOffset && "PHIs are unsplittable");
+    assert(EndOffset <= NewAllocaEndOffset && "PHIs are unsplittable");
+
+    // We would like to compute a new pointer in only one place, but have it be
+    // as local as possible to the PHI. To do that, we re-use the location of
+    // the old pointer, which necessarily must be in the right position to
+    // dominate the PHI.
+    IRBuilderBase::InsertPointGuard Guard(IRB);
+    if (isa<PHINode>(OldPtr))
+      IRB.SetInsertPoint(&*OldPtr->getParent()->getFirstInsertionPt());
+    else
+      IRB.SetInsertPoint(OldPtr);
+    IRB.SetCurrentDebugLocation(OldPtr->getDebugLoc());
+
+    Value *NewPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
+    // Replace the operands which were using the old pointer.
+    std::replace(PN.op_begin(), PN.op_end(), cast<Value>(OldPtr), NewPtr);
+
+    LLVM_DEBUG(dbgs() << "          to: " << PN << "\n");
+    deleteIfTriviallyDead(OldPtr);
+
+    // Fix the alignment of any loads or stores using this PHI node.
+    fixLoadStoreAlign(PN);
+
+    // PHIs can't be promoted on their own, but often can be speculated. We
+    // check the speculation outside of the rewriter so that we see the
+    // fully-rewritten alloca.
+    PHIUsers.insert(&PN);
+    return true;
+  }
+
+  bool visitSelectInst(SelectInst &SI) {
+    LLVM_DEBUG(dbgs() << "    original: " << SI << "\n");
+    assert((SI.getTrueValue() == OldPtr || SI.getFalseValue() == OldPtr) &&
+           "Pointer isn't an operand!");
+    assert(BeginOffset >= NewAllocaBeginOffset && "Selects are unsplittable");
+    assert(EndOffset <= NewAllocaEndOffset && "Selects are unsplittable");
+
+    Value *NewPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
+    // Replace the operands which were using the old pointer.
+    if (SI.getOperand(1) == OldPtr)
+      SI.setOperand(1, NewPtr);
+    if (SI.getOperand(2) == OldPtr)
+      SI.setOperand(2, NewPtr);
+
+    LLVM_DEBUG(dbgs() << "          to: " << SI << "\n");
+    deleteIfTriviallyDead(OldPtr);
+
+    // Fix the alignment of any loads or stores using this select.
+    fixLoadStoreAlign(SI);
+
+    // Selects can't be promoted on their own, but often can be speculated. We
+    // check the speculation outside of the rewriter so that we see the
+    // fully-rewritten alloca.
+    SelectUsers.insert(&SI);
+    return true;
+  }
+};
+
+namespace {
+
+/// Visitor to rewrite aggregate loads and stores as scalar.
+///
+/// This pass aggressively rewrites all aggregate loads and stores on
+/// a particular pointer (or any pointer derived from it which we can identify)
+/// with scalar loads and stores.
+class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
+  // Befriend the base class so it can delegate to private visit methods.
+  friend class InstVisitor<AggLoadStoreRewriter, bool>;
+
+  /// Queue of pointer uses to analyze and potentially rewrite.
+  SmallVector<Use *, 8> Queue;
+
+  /// Set to prevent us from cycling with phi nodes and loops.
+  SmallPtrSet<User *, 8> Visited;
+
+  /// The current pointer use being rewritten. This is used to dig up the used
+  /// value (as opposed to the user).
+  Use *U = nullptr;
+
+  /// Used to calculate offsets, and hence alignment, of subobjects.
+  const DataLayout &DL;
+
+  IRBuilderTy &IRB;
+
+public:
+  AggLoadStoreRewriter(const DataLayout &DL, IRBuilderTy &IRB)
+      : DL(DL), IRB(IRB) {}
+
+  /// Rewrite loads and stores through a pointer and all pointers derived from
+  /// it.
+  bool rewrite(Instruction &I) {
+    LLVM_DEBUG(dbgs() << "  Rewriting FCA loads and stores...\n");
+    enqueueUsers(I);
+    bool Changed = false;
+    while (!Queue.empty()) {
+      U = Queue.pop_back_val();
+      Changed |= visit(cast<Instruction>(U->getUser()));
+    }
+    return Changed;
+  }
+
+private:
+  /// Enqueue all the users of the given instruction for further processing.
+  /// This uses a set to de-duplicate users.
+  void enqueueUsers(Instruction &I) {
+    for (Use &U : I.uses())
+      if (Visited.insert(U.getUser()).second)
+        Queue.push_back(&U);
+  }
+
+  // Conservative default is to not rewrite anything.
+  bool visitInstruction(Instruction &I) { return false; }
+
+  /// Generic recursive split emission class.
+  template <typename Derived> class OpSplitter {
+  protected:
+    /// The builder used to form new instructions.
+    IRBuilderTy &IRB;
+
+    /// The indices which to be used with insert- or extractvalue to select the
+    /// appropriate value within the aggregate.
+    SmallVector<unsigned, 4> Indices;
+
+    /// The indices to a GEP instruction which will move Ptr to the correct slot
+    /// within the aggregate.
+    SmallVector<Value *, 4> GEPIndices;
+
+    /// The base pointer of the original op, used as a base for GEPing the
+    /// split operations.
+    Value *Ptr;
+
+    /// The base pointee type being GEPed into.
+    Type *BaseTy;
+
+    /// Known alignment of the base pointer.
+    Align BaseAlign;
+
+    /// To calculate offset of each component so we can correctly deduce
+    /// alignments.
+    const DataLayout &DL;
+
+    /// Initialize the splitter with an insertion point, Ptr and start with a
+    /// single zero GEP index.
+    OpSplitter(Instruction *InsertionPoint, Value *Ptr, Type *BaseTy,
+               Align BaseAlign, const DataLayout &DL, IRBuilderTy &IRB)
+        : IRB(IRB), GEPIndices(1, IRB.getInt32(0)), Ptr(Ptr), BaseTy(BaseTy),
+          BaseAlign(BaseAlign), DL(DL) {
+      IRB.SetInsertPoint(InsertionPoint);
+    }
+
+  public:
+    /// Generic recursive split emission routine.
+    ///
+    /// This method recursively splits an aggregate op (load or store) into
+    /// scalar or vector ops. It splits recursively until it hits a single value
+    /// and emits that single value operation via the template argument.
+    ///
+    /// The logic of this routine relies on GEPs and insertvalue and
+    /// extractvalue all operating with the same fundamental index list, merely
+    /// formatted differently (GEPs need actual values).
+    ///
+    /// \param Ty  The type being split recursively into smaller ops.
+    /// \param Agg The aggregate value being built up or stored, depending on
+    /// whether this is splitting a load or a store respectively.
+    void emitSplitOps(Type *Ty, Value *&Agg, const Twine &Name) {
+      if (Ty->isSingleValueType()) {
+        unsigned Offset = DL.getIndexedOffsetInType(BaseTy, GEPIndices);
+        return static_cast<Derived *>(this)->emitFunc(
+            Ty, Agg, commonAlignment(BaseAlign, Offset), Name);
+      }
+
+      if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+        unsigned OldSize = Indices.size();
+        (void)OldSize;
+        for (unsigned Idx = 0, Size = ATy->getNumElements(); Idx != Size;
+             ++Idx) {
+          assert(Indices.size() == OldSize && "Did not return to the old size");
+          Indices.push_back(Idx);
+          GEPIndices.push_back(IRB.getInt32(Idx));
+          emitSplitOps(ATy->getElementType(), Agg, Name + "." + Twine(Idx));
+          GEPIndices.pop_back();
+          Indices.pop_back();
+        }
+        return;
+      }
+
+      if (StructType *STy = dyn_cast<StructType>(Ty)) {
+        unsigned OldSize = Indices.size();
+        (void)OldSize;
+        for (unsigned Idx = 0, Size = STy->getNumElements(); Idx != Size;
+             ++Idx) {
+          assert(Indices.size() == OldSize && "Did not return to the old size");
+          Indices.push_back(Idx);
+          GEPIndices.push_back(IRB.getInt32(Idx));
+          emitSplitOps(STy->getElementType(Idx), Agg, Name + "." + Twine(Idx));
+          GEPIndices.pop_back();
+          Indices.pop_back();
+        }
+        return;
+      }
+
+      llvm_unreachable("Only arrays and structs are aggregate loadable types");
+    }
+  };
+
+  struct LoadOpSplitter : public OpSplitter<LoadOpSplitter> {
+    AAMDNodes AATags;
+
+    LoadOpSplitter(Instruction *InsertionPoint, Value *Ptr, Type *BaseTy,
+                   AAMDNodes AATags, Align BaseAlign, const DataLayout &DL,
+                   IRBuilderTy &IRB)
+        : OpSplitter<LoadOpSplitter>(InsertionPoint, Ptr, BaseTy, BaseAlign, DL,
+                                     IRB),
+          AATags(AATags) {}
+
+    /// Emit a leaf load of a single value. This is called at the leaves of the
+    /// recursive emission to actually load values.
+    void emitFunc(Type *Ty, Value *&Agg, Align Alignment, const Twine &Name) {
+      assert(Ty->isSingleValueType());
+      // Load the single value and insert it using the indices.
+      Value *GEP =
+          IRB.CreateInBoundsGEP(BaseTy, Ptr, GEPIndices, Name + ".gep");
+      LoadInst *Load =
+          IRB.CreateAlignedLoad(Ty, GEP, Alignment, Name + ".load");
+
+      APInt Offset(
+          DL.getIndexSizeInBits(Ptr->getType()->getPointerAddressSpace()), 0);
+      if (AATags &&
+          GEPOperator::accumulateConstantOffset(BaseTy, GEPIndices, DL, Offset))
+        Load->setAAMetadata(AATags.shift(Offset.getZExtValue()));
+
+      Agg = IRB.CreateInsertValue(Agg, Load, Indices, Name + ".insert");
+      LLVM_DEBUG(dbgs() << "          to: " << *Load << "\n");
+    }
+  };
+
+  bool visitLoadInst(LoadInst &LI) {
+    assert(LI.getPointerOperand() == *U);
+    if (!LI.isSimple() || LI.getType()->isSingleValueType())
+      return false;
+
+    // We have an aggregate being loaded, split it apart.
+    LLVM_DEBUG(dbgs() << "    original: " << LI << "\n");
+    LoadOpSplitter Splitter(&LI, *U, LI.getType(), LI.getAAMetadata(),
+                            getAdjustedAlignment(&LI, 0), DL, IRB);
+    Value *V = PoisonValue::get(LI.getType());
+    Splitter.emitSplitOps(LI.getType(), V, LI.getName() + ".fca");
+    Visited.erase(&LI);
+    LI.replaceAllUsesWith(V);
+    LI.eraseFromParent();
+    return true;
+  }
+
+  struct StoreOpSplitter : public OpSplitter<StoreOpSplitter> {
+    StoreOpSplitter(Instruction *InsertionPoint, Value *Ptr, Type *BaseTy,
+                    AAMDNodes AATags, StoreInst *AggStore, Align BaseAlign,
+                    const DataLayout &DL, IRBuilderTy &IRB)
+        : OpSplitter<StoreOpSplitter>(InsertionPoint, Ptr, BaseTy, BaseAlign,
+                                      DL, IRB),
+          AATags(AATags), AggStore(AggStore) {}
+    AAMDNodes AATags;
+    StoreInst *AggStore;
+    /// Emit a leaf store of a single value. This is called at the leaves of the
+    /// recursive emission to actually produce stores.
+    void emitFunc(Type *Ty, Value *&Agg, Align Alignment, const Twine &Name) {
+      assert(Ty->isSingleValueType());
+      // Extract the single value and store it using the indices.
+      //
+      // The gep and extractvalue values are factored out of the CreateStore
+      // call to make the output independent of the argument evaluation order.
+      Value *ExtractValue =
+          IRB.CreateExtractValue(Agg, Indices, Name + ".extract");
+      Value *InBoundsGEP =
+          IRB.CreateInBoundsGEP(BaseTy, Ptr, GEPIndices, Name + ".gep");
+      StoreInst *Store =
+          IRB.CreateAlignedStore(ExtractValue, InBoundsGEP, Alignment);
+
+      APInt Offset(
+          DL.getIndexSizeInBits(Ptr->getType()->getPointerAddressSpace()), 0);
+      if (AATags &&
+          GEPOperator::accumulateConstantOffset(BaseTy, GEPIndices, DL, Offset))
+        Store->setAAMetadata(AATags.shift(Offset.getZExtValue()));
+
+      // migrateDebugInfo requires the base Alloca. Walk to it from this gep.
+      // If we cannot (because there's an intervening non-const or unbounded
+      // gep) then we wouldn't expect to see dbg.assign intrinsics linked to
+      // this instruction.
+      APInt OffsetInBytes(DL.getTypeSizeInBits(Ptr->getType()), false);
+      Value *Base = InBoundsGEP->stripAndAccumulateInBoundsConstantOffsets(
+          DL, OffsetInBytes);
+      if (auto *OldAI = dyn_cast<AllocaInst>(Base)) {
+        uint64_t SizeInBits =
+            DL.getTypeSizeInBits(Store->getValueOperand()->getType());
+        migrateDebugInfo(OldAI, OffsetInBytes.getZExtValue() * 8, SizeInBits,
+                         AggStore, Store, Store->getPointerOperand(),
+                         Store->getValueOperand(), DL);
+      } else {
+        assert(at::getAssignmentMarkers(Store).empty() &&
+               "AT: unexpected debug.assign linked to store through "
+               "unbounded GEP");
+      }
+      LLVM_DEBUG(dbgs() << "          to: " << *Store << "\n");
+    }
+  };
+
+  bool visitStoreInst(StoreInst &SI) {
+    if (!SI.isSimple() || SI.getPointerOperand() != *U)
+      return false;
+    Value *V = SI.getValueOperand();
+    if (V->getType()->isSingleValueType())
+      return false;
+
+    // We have an aggregate being stored, split it apart.
+    LLVM_DEBUG(dbgs() << "    original: " << SI << "\n");
+    StoreOpSplitter Splitter(&SI, *U, V->getType(), SI.getAAMetadata(), &SI,
+                             getAdjustedAlignment(&SI, 0), DL, IRB);
+    Splitter.emitSplitOps(V->getType(), V, V->getName() + ".fca");
+    Visited.erase(&SI);
+    SI.eraseFromParent();
+    return true;
+  }
+
+  bool visitBitCastInst(BitCastInst &BC) {
+    enqueueUsers(BC);
+    return false;
+  }
+
+  bool visitAddrSpaceCastInst(AddrSpaceCastInst &ASC) {
+    enqueueUsers(ASC);
+    return false;
+  }
+
+  // Fold gep (select cond, ptr1, ptr2) => select cond, gep(ptr1), gep(ptr2)
+  bool foldGEPSelect(GetElementPtrInst &GEPI) {
+    if (!GEPI.hasAllConstantIndices())
+      return false;
+
+    SelectInst *Sel = cast<SelectInst>(GEPI.getPointerOperand());
+
+    LLVM_DEBUG(dbgs() << "  Rewriting gep(select) -> select(gep):"
+                      << "\n    original: " << *Sel
+                      << "\n              " << GEPI);
+
+    IRB.SetInsertPoint(&GEPI);
+    SmallVector<Value *, 4> Index(GEPI.indices());
+    bool IsInBounds = GEPI.isInBounds();
+
+    Type *Ty = GEPI.getSourceElementType();
+    Value *True = Sel->getTrueValue();
+    Value *NTrue = IRB.CreateGEP(Ty, True, Index, True->getName() + ".sroa.gep",
+                                 IsInBounds);
+
+    Value *False = Sel->getFalseValue();
+
+    Value *NFalse = IRB.CreateGEP(Ty, False, Index,
+                                  False->getName() + ".sroa.gep", IsInBounds);
+
+    Value *NSel = IRB.CreateSelect(Sel->getCondition(), NTrue, NFalse,
+                                   Sel->getName() + ".sroa.sel");
+    Visited.erase(&GEPI);
+    GEPI.replaceAllUsesWith(NSel);
+    GEPI.eraseFromParent();
+    Instruction *NSelI = cast<Instruction>(NSel);
+    Visited.insert(NSelI);
+    enqueueUsers(*NSelI);
+
+    LLVM_DEBUG(dbgs() << "\n          to: " << *NTrue
+                      << "\n              " << *NFalse
+                      << "\n              " << *NSel << '\n');
+
+    return true;
+  }
+
+  // Fold gep (phi ptr1, ptr2) => phi gep(ptr1), gep(ptr2)
+  bool foldGEPPhi(GetElementPtrInst &GEPI) {
+    if (!GEPI.hasAllConstantIndices())
+      return false;
+
+    PHINode *PHI = cast<PHINode>(GEPI.getPointerOperand());
+    if (GEPI.getParent() != PHI->getParent() ||
+        llvm::any_of(PHI->incoming_values(), [](Value *In)
+          { Instruction *I = dyn_cast<Instruction>(In);
+            return !I || isa<GetElementPtrInst>(I) || isa<PHINode>(I) ||
+                   succ_empty(I->getParent()) ||
+                   !I->getParent()->isLegalToHoistInto();
+          }))
+      return false;
+
+    LLVM_DEBUG(dbgs() << "  Rewriting gep(phi) -> phi(gep):"
+                      << "\n    original: " << *PHI
+                      << "\n              " << GEPI
+                      << "\n          to: ");
+
+    SmallVector<Value *, 4> Index(GEPI.indices());
+    bool IsInBounds = GEPI.isInBounds();
+    IRB.SetInsertPoint(GEPI.getParent()->getFirstNonPHI());
+    PHINode *NewPN = IRB.CreatePHI(GEPI.getType(), PHI->getNumIncomingValues(),
+                                   PHI->getName() + ".sroa.phi");
+    for (unsigned I = 0, E = PHI->getNumIncomingValues(); I != E; ++I) {
+      BasicBlock *B = PHI->getIncomingBlock(I);
+      Value *NewVal = nullptr;
+      int Idx = NewPN->getBasicBlockIndex(B);
+      if (Idx >= 0) {
+        NewVal = NewPN->getIncomingValue(Idx);
+      } else {
+        Instruction *In = cast<Instruction>(PHI->getIncomingValue(I));
+
+        IRB.SetInsertPoint(In->getParent(), std::next(In->getIterator()));
+        Type *Ty = GEPI.getSourceElementType();
+        NewVal = IRB.CreateGEP(Ty, In, Index, In->getName() + ".sroa.gep",
+                               IsInBounds);
+      }
+      NewPN->addIncoming(NewVal, B);
+    }
+
+    Visited.erase(&GEPI);
+    GEPI.replaceAllUsesWith(NewPN);
+    GEPI.eraseFromParent();
+    Visited.insert(NewPN);
+    enqueueUsers(*NewPN);
+
+    LLVM_DEBUG(for (Value *In : NewPN->incoming_values())
+                 dbgs() << "\n              " << *In;
+               dbgs() << "\n              " << *NewPN << '\n');
+
+    return true;
+  }
+
+  bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
+    if (isa<SelectInst>(GEPI.getPointerOperand()) &&
+        foldGEPSelect(GEPI))
+      return true;
+
+    if (isa<PHINode>(GEPI.getPointerOperand()) &&
+        foldGEPPhi(GEPI))
+      return true;
+
+    enqueueUsers(GEPI);
+    return false;
+  }
+
+  bool visitPHINode(PHINode &PN) {
+    enqueueUsers(PN);
+    return false;
+  }
+
+  bool visitSelectInst(SelectInst &SI) {
+    enqueueUsers(SI);
+    return false;
+  }
+};
+
+} // end anonymous namespace
+
+/// Strip aggregate type wrapping.
+///
+/// This removes no-op aggregate types wrapping an underlying type. It will
+/// strip as many layers of types as it can without changing either the type
+/// size or the allocated size.
+static Type *stripAggregateTypeWrapping(const DataLayout &DL, Type *Ty) {
+  if (Ty->isSingleValueType())
+    return Ty;
+
+  uint64_t AllocSize = DL.getTypeAllocSize(Ty).getFixedValue();
+  uint64_t TypeSize = DL.getTypeSizeInBits(Ty).getFixedValue();
+
+  Type *InnerTy;
+  if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
+    InnerTy = ArrTy->getElementType();
+  } else if (StructType *STy = dyn_cast<StructType>(Ty)) {
+    const StructLayout *SL = DL.getStructLayout(STy);
+    unsigned Index = SL->getElementContainingOffset(0);
+    InnerTy = STy->getElementType(Index);
+  } else {
+    return Ty;
+  }
+
+  if (AllocSize > DL.getTypeAllocSize(InnerTy).getFixedValue() ||
+      TypeSize > DL.getTypeSizeInBits(InnerTy).getFixedValue())
+    return Ty;
+
+  return stripAggregateTypeWrapping(DL, InnerTy);
+}
+
+/// Try to find a partition of the aggregate type passed in for a given
+/// offset and size.
+///
+/// This recurses through the aggregate type and tries to compute a subtype
+/// based on the offset and size. When the offset and size span a sub-section
+/// of an array, it will even compute a new array type for that sub-section,
+/// and the same for structs.
+///
+/// Note that this routine is very strict and tries to find a partition of the
+/// type which produces the *exact* right offset and size. It is not forgiving
+/// when the size or offset cause either end of type-based partition to be off.
+/// Also, this is a best-effort routine. It is reasonable to give up and not
+/// return a type if necessary.
+static Type *getTypePartition(const DataLayout &DL, Type *Ty, uint64_t Offset,
+                              uint64_t Size) {
+  if (Offset == 0 && DL.getTypeAllocSize(Ty).getFixedValue() == Size)
+    return stripAggregateTypeWrapping(DL, Ty);
+  if (Offset > DL.getTypeAllocSize(Ty).getFixedValue() ||
+      (DL.getTypeAllocSize(Ty).getFixedValue() - Offset) < Size)
+    return nullptr;
+
+  if (isa<ArrayType>(Ty) || isa<VectorType>(Ty)) {
+     Type *ElementTy;
+     uint64_t TyNumElements;
+     if (auto *AT = dyn_cast<ArrayType>(Ty)) {
+       ElementTy = AT->getElementType();
+       TyNumElements = AT->getNumElements();
+     } else {
+       // FIXME: This isn't right for vectors with non-byte-sized or
+       // non-power-of-two sized elements.
+       auto *VT = cast<FixedVectorType>(Ty);
+       ElementTy = VT->getElementType();
+       TyNumElements = VT->getNumElements();
+    }
+    uint64_t ElementSize = DL.getTypeAllocSize(ElementTy).getFixedValue();
+    uint64_t NumSkippedElements = Offset / ElementSize;
+    if (NumSkippedElements >= TyNumElements)
+      return nullptr;
+    Offset -= NumSkippedElements * ElementSize;
+
+    // First check if we need to recurse.
+    if (Offset > 0 || Size < ElementSize) {
+      // Bail if the partition ends in a different array element.
+      if ((Offset + Size) > ElementSize)
+        return nullptr;
+      // Recurse through the element type trying to peel off offset bytes.
+      return getTypePartition(DL, ElementTy, Offset, Size);
+    }
+    assert(Offset == 0);
+
+    if (Size == ElementSize)
+      return stripAggregateTypeWrapping(DL, ElementTy);
+    assert(Size > ElementSize);
+    uint64_t NumElements = Size / ElementSize;
+    if (NumElements * ElementSize != Size)
+      return nullptr;
+    return ArrayType::get(ElementTy, NumElements);
+  }
+
+  StructType *STy = dyn_cast<StructType>(Ty);
+  if (!STy)
+    return nullptr;
+
+  const StructLayout *SL = DL.getStructLayout(STy);
+  if (Offset >= SL->getSizeInBytes())
+    return nullptr;
+  uint64_t EndOffset = Offset + Size;
+  if (EndOffset > SL->getSizeInBytes())
+    return nullptr;
+
+  unsigned Index = SL->getElementContainingOffset(Offset);
+  Offset -= SL->getElementOffset(Index);
+
+  Type *ElementTy = STy->getElementType(Index);
+  uint64_t ElementSize = DL.getTypeAllocSize(ElementTy).getFixedValue();
+  if (Offset >= ElementSize)
+    return nullptr; // The offset points into alignment padding.
+
+  // See if any partition must be contained by the element.
+  if (Offset > 0 || Size < ElementSize) {
+    if ((Offset + Size) > ElementSize)
+      return nullptr;
+    return getTypePartition(DL, ElementTy, Offset, Size);
+  }
+  assert(Offset == 0);
+
+  if (Size == ElementSize)
+    return stripAggregateTypeWrapping(DL, ElementTy);
+
+  StructType::element_iterator EI = STy->element_begin() + Index,
+                               EE = STy->element_end();
+  if (EndOffset < SL->getSizeInBytes()) {
+    unsigned EndIndex = SL->getElementContainingOffset(EndOffset);
+    if (Index == EndIndex)
+      return nullptr; // Within a single element and its padding.
+
+    // Don't try to form "natural" types if the elements don't line up with the
+    // expected size.
+    // FIXME: We could potentially recurse down through the last element in the
+    // sub-struct to find a natural end point.
+    if (SL->getElementOffset(EndIndex) != EndOffset)
+      return nullptr;
+
+    assert(Index < EndIndex);
+    EE = STy->element_begin() + EndIndex;
+  }
+
+  // Try to build up a sub-structure.
+  StructType *SubTy =
+      StructType::get(STy->getContext(), ArrayRef(EI, EE), STy->isPacked());
+  const StructLayout *SubSL = DL.getStructLayout(SubTy);
+  if (Size != SubSL->getSizeInBytes())
+    return nullptr; // The sub-struct doesn't have quite the size needed.
+
+  return SubTy;
+}
+
+/// Pre-split loads and stores to simplify rewriting.
+///
+/// We want to break up the splittable load+store pairs as much as
+/// possible. This is important to do as a preprocessing step, as once we
+/// start rewriting the accesses to partitions of the alloca we lose the
+/// necessary information to correctly split apart paired loads and stores
+/// which both point into this alloca. The case to consider is something like
+/// the following:
+///
+///   %a = alloca [12 x i8]
+///   %gep1 = getelementptr i8, ptr %a, i32 0
+///   %gep2 = getelementptr i8, ptr %a, i32 4
+///   %gep3 = getelementptr i8, ptr %a, i32 8
+///   store float 0.0, ptr %gep1
+///   store float 1.0, ptr %gep2
+///   %v = load i64, ptr %gep1
+///   store i64 %v, ptr %gep2
+///   %f1 = load float, ptr %gep2
+///   %f2 = load float, ptr %gep3
+///
+/// Here we want to form 3 partitions of the alloca, each 4 bytes large, and
+/// promote everything so we recover the 2 SSA values that should have been
+/// there all along.
+///
+/// \returns true if any changes are made.
+bool SROAPass::presplitLoadsAndStores(AllocaInst &AI, AllocaSlices &AS) {
+  LLVM_DEBUG(dbgs() << "Pre-splitting loads and stores\n");
+
+  // Track the loads and stores which are candidates for pre-splitting here, in
+  // the order they first appear during the partition scan. These give stable
+  // iteration order and a basis for tracking which loads and stores we
+  // actually split.
+  SmallVector<LoadInst *, 4> Loads;
+  SmallVector<StoreInst *, 4> Stores;
+
+  // We need to accumulate the splits required of each load or store where we
+  // can find them via a direct lookup. This is important to cross-check loads
+  // and stores against each other. We also track the slice so that we can kill
+  // all the slices that end up split.
+  struct SplitOffsets {
+    Slice *S;
+    std::vector<uint64_t> Splits;
+  };
+  SmallDenseMap<Instruction *, SplitOffsets, 8> SplitOffsetsMap;
+
+  // Track loads out of this alloca which cannot, for any reason, be pre-split.
+  // This is important as we also cannot pre-split stores of those loads!
+  // FIXME: This is all pretty gross. It means that we can be more aggressive
+  // in pre-splitting when the load feeding the store happens to come from
+  // a separate alloca. Put another way, the effectiveness of SROA would be
+  // decreased by a frontend which just concatenated all of its local allocas
+  // into one big flat alloca. But defeating such patterns is exactly the job
+  // SROA is tasked with! Sadly, to not have this discrepancy we would have
+  // change store pre-splitting to actually force pre-splitting of the load
+  // that feeds it *and all stores*. That makes pre-splitting much harder, but
+  // maybe it would make it more principled?
+  SmallPtrSet<LoadInst *, 8> UnsplittableLoads;
+
+  LLVM_DEBUG(dbgs() << "  Searching for candidate loads and stores\n");
+  for (auto &P : AS.partitions()) {
+    for (Slice &S : P) {
+      Instruction *I = cast<Instruction>(S.getUse()->getUser());
+      if (!S.isSplittable() || S.endOffset() <= P.endOffset()) {
+        // If this is a load we have to track that it can't participate in any
+        // pre-splitting. If this is a store of a load we have to track that
+        // that load also can't participate in any pre-splitting.
+        if (auto *LI = dyn_cast<LoadInst>(I))
+          UnsplittableLoads.insert(LI);
+        else if (auto *SI = dyn_cast<StoreInst>(I))
+          if (auto *LI = dyn_cast<LoadInst>(SI->getValueOperand()))
+            UnsplittableLoads.insert(LI);
+        continue;
+      }
+      assert(P.endOffset() > S.beginOffset() &&
+             "Empty or backwards partition!");
+
+      // Determine if this is a pre-splittable slice.
+      if (auto *LI = dyn_cast<LoadInst>(I)) {
+        assert(!LI->isVolatile() && "Cannot split volatile loads!");
+
+        // The load must be used exclusively to store into other pointers for
+        // us to be able to arbitrarily pre-split it. The stores must also be
+        // simple to avoid changing semantics.
+        auto IsLoadSimplyStored = [](LoadInst *LI) {
+          for (User *LU : LI->users()) {
+            auto *SI = dyn_cast<StoreInst>(LU);
+            if (!SI || !SI->isSimple())
+              return false;
+          }
+          return true;
+        };
+        if (!IsLoadSimplyStored(LI)) {
+          UnsplittableLoads.insert(LI);
+          continue;
+        }
+
+        Loads.push_back(LI);
+      } else if (auto *SI = dyn_cast<StoreInst>(I)) {
+        if (S.getUse() != &SI->getOperandUse(SI->getPointerOperandIndex()))
+          // Skip stores *of* pointers. FIXME: This shouldn't even be possible!
+          continue;
+        auto *StoredLoad = dyn_cast<LoadInst>(SI->getValueOperand());
+        if (!StoredLoad || !StoredLoad->isSimple())
+          continue;
+        assert(!SI->isVolatile() && "Cannot split volatile stores!");
+
+        Stores.push_back(SI);
+      } else {
+        // Other uses cannot be pre-split.
+        continue;
+      }
+
+      // Record the initial split.
+      LLVM_DEBUG(dbgs() << "    Candidate: " << *I << "\n");
+      auto &Offsets = SplitOffsetsMap[I];
+      assert(Offsets.Splits.empty() &&
+             "Should not have splits the first time we see an instruction!");
+      Offsets.S = &S;
+      Offsets.Splits.push_back(P.endOffset() - S.beginOffset());
+    }
+
+    // Now scan the already split slices, and add a split for any of them which
+    // we're going to pre-split.
+    for (Slice *S : P.splitSliceTails()) {
+      auto SplitOffsetsMapI =
+          SplitOffsetsMap.find(cast<Instruction>(S->getUse()->getUser()));
+      if (SplitOffsetsMapI == SplitOffsetsMap.end())
+        continue;
+      auto &Offsets = SplitOffsetsMapI->second;
+
+      assert(Offsets.S == S && "Found a mismatched slice!");
+      assert(!Offsets.Splits.empty() &&
+             "Cannot have an empty set of splits on the second partition!");
+      assert(Offsets.Splits.back() ==
+                 P.beginOffset() - Offsets.S->beginOffset() &&
+             "Previous split does not end where this one begins!");
+
+      // Record each split. The last partition's end isn't needed as the size
+      // of the slice dictates that.
+      if (S->endOffset() > P.endOffset())
+        Offsets.Splits.push_back(P.endOffset() - Offsets.S->beginOffset());
+    }
+  }
+
+  // We may have split loads where some of their stores are split stores. For
+  // such loads and stores, we can only pre-split them if their splits exactly
+  // match relative to their starting offset. We have to verify this prior to
+  // any rewriting.
+  llvm::erase_if(Stores, [&UnsplittableLoads, &SplitOffsetsMap](StoreInst *SI) {
+    // Lookup the load we are storing in our map of split
+    // offsets.
+    auto *LI = cast<LoadInst>(SI->getValueOperand());
+    // If it was completely unsplittable, then we're done,
+    // and this store can't be pre-split.
+    if (UnsplittableLoads.count(LI))
+      return true;
+
+    auto LoadOffsetsI = SplitOffsetsMap.find(LI);
+    if (LoadOffsetsI == SplitOffsetsMap.end())
+      return false; // Unrelated loads are definitely safe.
+    auto &LoadOffsets = LoadOffsetsI->second;
+
+    // Now lookup the store's offsets.
+    auto &StoreOffsets = SplitOffsetsMap[SI];
+
+    // If the relative offsets of each split in the load and
+    // store match exactly, then we can split them and we
+    // don't need to remove them here.
+    if (LoadOffsets.Splits == StoreOffsets.Splits)
+      return false;
+
+    LLVM_DEBUG(dbgs() << "    Mismatched splits for load and store:\n"
+                      << "      " << *LI << "\n"
+                      << "      " << *SI << "\n");
+
+    // We've found a store and load that we need to split
+    // with mismatched relative splits. Just give up on them
+    // and remove both instructions from our list of
+    // candidates.
+    UnsplittableLoads.insert(LI);
+    return true;
+  });
+  // Now we have to go *back* through all the stores, because a later store may
+  // have caused an earlier store's load to become unsplittable and if it is
+  // unsplittable for the later store, then we can't rely on it being split in
+  // the earlier store either.
+  llvm::erase_if(Stores, [&UnsplittableLoads](StoreInst *SI) {
+    auto *LI = cast<LoadInst>(SI->getValueOperand());
+    return UnsplittableLoads.count(LI);
+  });
+  // Once we've established all the loads that can't be split for some reason,
+  // filter any that made it into our list out.
+  llvm::erase_if(Loads, [&UnsplittableLoads](LoadInst *LI) {
+    return UnsplittableLoads.count(LI);
+  });
+
+  // If no loads or stores are left, there is no pre-splitting to be done for
+  // this alloca.
+  if (Loads.empty() && Stores.empty())
+    return false;
+
+  // From here on, we can't fail and will be building new accesses, so rig up
+  // an IR builder.
+  IRBuilderTy IRB(&AI);
+
+  // Collect the new slices which we will merge into the alloca slices.
+  SmallVector<Slice, 4> NewSlices;
+
+  // Track any allocas we end up splitting loads and stores for so we iterate
+  // on them.
+  SmallPtrSet<AllocaInst *, 4> ResplitPromotableAllocas;
+
+  // At this point, we have collected all of the loads and stores we can
+  // pre-split, and the specific splits needed for them. We actually do the
+  // splitting in a specific order in order to handle when one of the loads in
+  // the value operand to one of the stores.
+  //
+  // First, we rewrite all of the split loads, and just accumulate each split
+  // load in a parallel structure. We also build the slices for them and append
+  // them to the alloca slices.
+  SmallDenseMap<LoadInst *, std::vector<LoadInst *>, 1> SplitLoadsMap;
+  std::vector<LoadInst *> SplitLoads;
+  const DataLayout &DL = AI.getModule()->getDataLayout();
+  for (LoadInst *LI : Loads) {
+    SplitLoads.clear();
+
+    auto &Offsets = SplitOffsetsMap[LI];
+    unsigned SliceSize = Offsets.S->endOffset() - Offsets.S->beginOffset();
+    assert(LI->getType()->getIntegerBitWidth() % 8 == 0 &&
+           "Load must have type size equal to store size");
+    assert(LI->getType()->getIntegerBitWidth() / 8 >= SliceSize &&
+           "Load must be >= slice size");
+
+    uint64_t BaseOffset = Offsets.S->beginOffset();
+    assert(BaseOffset + SliceSize > BaseOffset &&
+           "Cannot represent alloca access size using 64-bit integers!");
+
+    Instruction *BasePtr = cast<Instruction>(LI->getPointerOperand());
+    IRB.SetInsertPoint(LI);
+
+    LLVM_DEBUG(dbgs() << "  Splitting load: " << *LI << "\n");
+
+    uint64_t PartOffset = 0, PartSize = Offsets.Splits.front();
+    int Idx = 0, Size = Offsets.Splits.size();
+    for (;;) {
+      auto *PartTy = Type::getIntNTy(LI->getContext(), PartSize * 8);
+      auto AS = LI->getPointerAddressSpace();
+      auto *PartPtrTy = PartTy->getPointerTo(AS);
+      LoadInst *PLoad = IRB.CreateAlignedLoad(
+          PartTy,
+          getAdjustedPtr(IRB, DL, BasePtr,
+                         APInt(DL.getIndexSizeInBits(AS), PartOffset),
+                         PartPtrTy, BasePtr->getName() + "."),
+          getAdjustedAlignment(LI, PartOffset),
+          /*IsVolatile*/ false, LI->getName());
+      PLoad->copyMetadata(*LI, {LLVMContext::MD_mem_parallel_loop_access,
+                                LLVMContext::MD_access_group});
+
+      // Append this load onto the list of split loads so we can find it later
+      // to rewrite the stores.
+      SplitLoads.push_back(PLoad);
+
+      // Now build a new slice for the alloca.
+      NewSlices.push_back(
+          Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize,
+                &PLoad->getOperandUse(PLoad->getPointerOperandIndex()),
+                /*IsSplittable*/ false));
+      LLVM_DEBUG(dbgs() << "    new slice [" << NewSlices.back().beginOffset()
+                        << ", " << NewSlices.back().endOffset()
+                        << "): " << *PLoad << "\n");
+
+      // See if we've handled all the splits.
+      if (Idx >= Size)
+        break;
+
+      // Setup the next partition.
+      PartOffset = Offsets.Splits[Idx];
+      ++Idx;
+      PartSize = (Idx < Size ? Offsets.Splits[Idx] : SliceSize) - PartOffset;
+    }
+
+    // Now that we have the split loads, do the slow walk over all uses of the
+    // load and rewrite them as split stores, or save the split loads to use
+    // below if the store is going to be split there anyways.
+    bool DeferredStores = false;
+    for (User *LU : LI->users()) {
+      StoreInst *SI = cast<StoreInst>(LU);
+      if (!Stores.empty() && SplitOffsetsMap.count(SI)) {
+        DeferredStores = true;
+        LLVM_DEBUG(dbgs() << "    Deferred splitting of store: " << *SI
+                          << "\n");
+        continue;
+      }
+
+      Value *StoreBasePtr = SI->getPointerOperand();
+      IRB.SetInsertPoint(SI);
+
+      LLVM_DEBUG(dbgs() << "    Splitting store of load: " << *SI << "\n");
+
+      for (int Idx = 0, Size = SplitLoads.size(); Idx < Size; ++Idx) {
+        LoadInst *PLoad = SplitLoads[Idx];
+        uint64_t PartOffset = Idx == 0 ? 0 : Offsets.Splits[Idx - 1];
+        auto *PartPtrTy =
+            PLoad->getType()->getPointerTo(SI->getPointerAddressSpace());
+
+        auto AS = SI->getPointerAddressSpace();
+        StoreInst *PStore = IRB.CreateAlignedStore(
+            PLoad,
+            getAdjustedPtr(IRB, DL, StoreBasePtr,
+                           APInt(DL.getIndexSizeInBits(AS), PartOffset),
+                           PartPtrTy, StoreBasePtr->getName() + "."),
+            getAdjustedAlignment(SI, PartOffset),
+            /*IsVolatile*/ false);
+        PStore->copyMetadata(*SI, {LLVMContext::MD_mem_parallel_loop_access,
+                                   LLVMContext::MD_access_group,
+                                   LLVMContext::MD_DIAssignID});
+        LLVM_DEBUG(dbgs() << "      +" << PartOffset << ":" << *PStore << "\n");
+      }
+
+      // We want to immediately iterate on any allocas impacted by splitting
+      // this store, and we have to track any promotable alloca (indicated by
+      // a direct store) as needing to be resplit because it is no longer
+      // promotable.
+      if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(StoreBasePtr)) {
+        ResplitPromotableAllocas.insert(OtherAI);
+        Worklist.insert(OtherAI);
+      } else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(
+                     StoreBasePtr->stripInBoundsOffsets())) {
+        Worklist.insert(OtherAI);
+      }
+
+      // Mark the original store as dead.
+      DeadInsts.push_back(SI);
+    }
+
+    // Save the split loads if there are deferred stores among the users.
+    if (DeferredStores)
+      SplitLoadsMap.insert(std::make_pair(LI, std::move(SplitLoads)));
+
+    // Mark the original load as dead and kill the original slice.
+    DeadInsts.push_back(LI);
+    Offsets.S->kill();
+  }
+
+  // Second, we rewrite all of the split stores. At this point, we know that
+  // all loads from this alloca have been split already. For stores of such
+  // loads, we can simply look up the pre-existing split loads. For stores of
+  // other loads, we split those loads first and then write split stores of
+  // them.
+  for (StoreInst *SI : Stores) {
+    auto *LI = cast<LoadInst>(SI->getValueOperand());
+    IntegerType *Ty = cast<IntegerType>(LI->getType());
+    assert(Ty->getBitWidth() % 8 == 0);
+    uint64_t StoreSize = Ty->getBitWidth() / 8;
+    assert(StoreSize > 0 && "Cannot have a zero-sized integer store!");
+
+    auto &Offsets = SplitOffsetsMap[SI];
+    assert(StoreSize == Offsets.S->endOffset() - Offsets.S->beginOffset() &&
+           "Slice size should always match load size exactly!");
+    uint64_t BaseOffset = Offsets.S->beginOffset();
+    assert(BaseOffset + StoreSize > BaseOffset &&
+           "Cannot represent alloca access size using 64-bit integers!");
+
+    Value *LoadBasePtr = LI->getPointerOperand();
+    Instruction *StoreBasePtr = cast<Instruction>(SI->getPointerOperand());
+
+    LLVM_DEBUG(dbgs() << "  Splitting store: " << *SI << "\n");
+
+    // Check whether we have an already split load.
+    auto SplitLoadsMapI = SplitLoadsMap.find(LI);
+    std::vector<LoadInst *> *SplitLoads = nullptr;
+    if (SplitLoadsMapI != SplitLoadsMap.end()) {
+      SplitLoads = &SplitLoadsMapI->second;
+      assert(SplitLoads->size() == Offsets.Splits.size() + 1 &&
+             "Too few split loads for the number of splits in the store!");
+    } else {
+      LLVM_DEBUG(dbgs() << "          of load: " << *LI << "\n");
+    }
+
+    uint64_t PartOffset = 0, PartSize = Offsets.Splits.front();
+    int Idx = 0, Size = Offsets.Splits.size();
+    for (;;) {
+      auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8);
+      auto *LoadPartPtrTy = PartTy->getPointerTo(LI->getPointerAddressSpace());
+      auto *StorePartPtrTy = PartTy->getPointerTo(SI->getPointerAddressSpace());
+
+      // Either lookup a split load or create one.
+      LoadInst *PLoad;
+      if (SplitLoads) {
+        PLoad = (*SplitLoads)[Idx];
+      } else {
+        IRB.SetInsertPoint(LI);
+        auto AS = LI->getPointerAddressSpace();
+        PLoad = IRB.CreateAlignedLoad(
+            PartTy,
+            getAdjustedPtr(IRB, DL, LoadBasePtr,
+                           APInt(DL.getIndexSizeInBits(AS), PartOffset),
+                           LoadPartPtrTy, LoadBasePtr->getName() + "."),
+            getAdjustedAlignment(LI, PartOffset),
+            /*IsVolatile*/ false, LI->getName());
+        PLoad->copyMetadata(*LI, {LLVMContext::MD_mem_parallel_loop_access,
+                                  LLVMContext::MD_access_group});
+      }
+
+      // And store this partition.
+      IRB.SetInsertPoint(SI);
+      auto AS = SI->getPointerAddressSpace();
+      StoreInst *PStore = IRB.CreateAlignedStore(
+          PLoad,
+          getAdjustedPtr(IRB, DL, StoreBasePtr,
+                         APInt(DL.getIndexSizeInBits(AS), PartOffset),
+                         StorePartPtrTy, StoreBasePtr->getName() + "."),
+          getAdjustedAlignment(SI, PartOffset),
+          /*IsVolatile*/ false);
+      PStore->copyMetadata(*SI, {LLVMContext::MD_mem_parallel_loop_access,
+                                 LLVMContext::MD_access_group});
+
+      // Now build a new slice for the alloca.
+      NewSlices.push_back(
+          Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize,
+                &PStore->getOperandUse(PStore->getPointerOperandIndex()),
+                /*IsSplittable*/ false));
+      LLVM_DEBUG(dbgs() << "    new slice [" << NewSlices.back().beginOffset()
+                        << ", " << NewSlices.back().endOffset()
+                        << "): " << *PStore << "\n");
+      if (!SplitLoads) {
+        LLVM_DEBUG(dbgs() << "      of split load: " << *PLoad << "\n");
+      }
+
+      // See if we've finished all the splits.
+      if (Idx >= Size)
+        break;
+
+      // Setup the next partition.
+      PartOffset = Offsets.Splits[Idx];
+      ++Idx;
+      PartSize = (Idx < Size ? Offsets.Splits[Idx] : StoreSize) - PartOffset;
+    }
+
+    // We want to immediately iterate on any allocas impacted by splitting
+    // this load, which is only relevant if it isn't a load of this alloca and
+    // thus we didn't already split the loads above. We also have to keep track
+    // of any promotable allocas we split loads on as they can no longer be
+    // promoted.
+    if (!SplitLoads) {
+      if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(LoadBasePtr)) {
+        assert(OtherAI != &AI && "We can't re-split our own alloca!");
+        ResplitPromotableAllocas.insert(OtherAI);
+        Worklist.insert(OtherAI);
+      } else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(
+                     LoadBasePtr->stripInBoundsOffsets())) {
+        assert(OtherAI != &AI && "We can't re-split our own alloca!");
+        Worklist.insert(OtherAI);
+      }
+    }
+
+    // Mark the original store as dead now that we've split it up and kill its
+    // slice. Note that we leave the original load in place unless this store
+    // was its only use. It may in turn be split up if it is an alloca load
+    // for some other alloca, but it may be a normal load. This may introduce
+    // redundant loads, but where those can be merged the rest of the optimizer
+    // should handle the merging, and this uncovers SSA splits which is more
+    // important. In practice, the original loads will almost always be fully
+    // split and removed eventually, and the splits will be merged by any
+    // trivial CSE, including instcombine.
+    if (LI->hasOneUse()) {
+      assert(*LI->user_begin() == SI && "Single use isn't this store!");
+      DeadInsts.push_back(LI);
+    }
+    DeadInsts.push_back(SI);
+    Offsets.S->kill();
+  }
+
+  // Remove the killed slices that have ben pre-split.
+  llvm::erase_if(AS, [](const Slice &S) { return S.isDead(); });
+
+  // Insert our new slices. This will sort and merge them into the sorted
+  // sequence.
+  AS.insert(NewSlices);
+
+  LLVM_DEBUG(dbgs() << "  Pre-split slices:\n");
+#ifndef NDEBUG
+  for (auto I = AS.begin(), E = AS.end(); I != E; ++I)
+    LLVM_DEBUG(AS.print(dbgs(), I, "    "));
+#endif
+
+  // Finally, don't try to promote any allocas that new require re-splitting.
+  // They have already been added to the worklist above.
+  llvm::erase_if(PromotableAllocas, [&](AllocaInst *AI) {
+    return ResplitPromotableAllocas.count(AI);
+  });
+
+  return true;
+}
+
+/// Rewrite an alloca partition's users.
+///
+/// This routine drives both of the rewriting goals of the SROA pass. It tries
+/// to rewrite uses of an alloca partition to be conducive for SSA value
+/// promotion. If the partition needs a new, more refined alloca, this will
+/// build that new alloca, preserving as much type information as possible, and
+/// rewrite the uses of the old alloca to point at the new one and have the
+/// appropriate new offsets. It also evaluates how successful the rewrite was
+/// at enabling promotion and if it was successful queues the alloca to be
+/// promoted.
+AllocaInst *SROAPass::rewritePartition(AllocaInst &AI, AllocaSlices &AS,
+                                       Partition &P) {
+  // Try to compute a friendly type for this partition of the alloca. This
+  // won't always succeed, in which case we fall back to a legal integer type
+  // or an i8 array of an appropriate size.
+  Type *SliceTy = nullptr;
+  VectorType *SliceVecTy = nullptr;
+  const DataLayout &DL = AI.getModule()->getDataLayout();
+  std::pair<Type *, IntegerType *> CommonUseTy =
+      findCommonType(P.begin(), P.end(), P.endOffset());
+  // Do all uses operate on the same type?
+  if (CommonUseTy.first)
+    if (DL.getTypeAllocSize(CommonUseTy.first).getFixedValue() >= P.size()) {
+      SliceTy = CommonUseTy.first;
+      SliceVecTy = dyn_cast<VectorType>(SliceTy);
+    }
+  // If not, can we find an appropriate subtype in the original allocated type?
+  if (!SliceTy)
+    if (Type *TypePartitionTy = getTypePartition(DL, AI.getAllocatedType(),
+                                                 P.beginOffset(), P.size()))
+      SliceTy = TypePartitionTy;
+
+  // If still not, can we use the largest bitwidth integer type used?
+  if (!SliceTy && CommonUseTy.second)
+    if (DL.getTypeAllocSize(CommonUseTy.second).getFixedValue() >= P.size()) {
+      SliceTy = CommonUseTy.second;
+      SliceVecTy = dyn_cast<VectorType>(SliceTy);
+    }
+  if ((!SliceTy || (SliceTy->isArrayTy() &&
+                    SliceTy->getArrayElementType()->isIntegerTy())) &&
+      DL.isLegalInteger(P.size() * 8)) {
+    SliceTy = Type::getIntNTy(*C, P.size() * 8);
+  }
+
+  // If the common use types are not viable for promotion then attempt to find
+  // another type that is viable.
+  if (SliceVecTy && !checkVectorTypeForPromotion(P, SliceVecTy, DL))
+    if (Type *TypePartitionTy = getTypePartition(DL, AI.getAllocatedType(),
+                                                 P.beginOffset(), P.size())) {
+      VectorType *TypePartitionVecTy = dyn_cast<VectorType>(TypePartitionTy);
+      if (TypePartitionVecTy &&
+          checkVectorTypeForPromotion(P, TypePartitionVecTy, DL))
+        SliceTy = TypePartitionTy;
+    }
+
+  if (!SliceTy)
+    SliceTy = ArrayType::get(Type::getInt8Ty(*C), P.size());
+  assert(DL.getTypeAllocSize(SliceTy).getFixedValue() >= P.size());
+
+  bool IsIntegerPromotable = isIntegerWideningViable(P, SliceTy, DL);
+
+  VectorType *VecTy =
+      IsIntegerPromotable ? nullptr : isVectorPromotionViable(P, DL);
+  if (VecTy)
+    SliceTy = VecTy;
+
+  // Check for the case where we're going to rewrite to a new alloca of the
+  // exact same type as the original, and with the same access offsets. In that
+  // case, re-use the existing alloca, but still run through the rewriter to
+  // perform phi and select speculation.
+  // P.beginOffset() can be non-zero even with the same type in a case with
+  // out-of-bounds access (e.g. @PR35657 function in SROA/basictest.ll).
+  AllocaInst *NewAI;
+  if (SliceTy == AI.getAllocatedType() && P.beginOffset() == 0) {
+    NewAI = &AI;
+    // FIXME: We should be able to bail at this point with "nothing changed".
+    // FIXME: We might want to defer PHI speculation until after here.
+    // FIXME: return nullptr;
+  } else {
+    // Make sure the alignment is compatible with P.beginOffset().
+    const Align Alignment = commonAlignment(AI.getAlign(), P.beginOffset());
+    // If we will get at least this much alignment from the type alone, leave
+    // the alloca's alignment unconstrained.
+    const bool IsUnconstrained = Alignment <= DL.getABITypeAlign(SliceTy);
+    NewAI = new AllocaInst(
+        SliceTy, AI.getAddressSpace(), nullptr,
+        IsUnconstrained ? DL.getPrefTypeAlign(SliceTy) : Alignment,
+        AI.getName() + ".sroa." + Twine(P.begin() - AS.begin()), &AI);
+    // Copy the old AI debug location over to the new one.
+    NewAI->setDebugLoc(AI.getDebugLoc());
+    ++NumNewAllocas;
+  }
+
+  LLVM_DEBUG(dbgs() << "Rewriting alloca partition "
+                    << "[" << P.beginOffset() << "," << P.endOffset()
+                    << ") to: " << *NewAI << "\n");
+
+  // Track the high watermark on the worklist as it is only relevant for
+  // promoted allocas. We will reset it to this point if the alloca is not in
+  // fact scheduled for promotion.
+  unsigned PPWOldSize = PostPromotionWorklist.size();
+  unsigned NumUses = 0;
+  SmallSetVector<PHINode *, 8> PHIUsers;
+  SmallSetVector<SelectInst *, 8> SelectUsers;
+
+  AllocaSliceRewriter Rewriter(DL, AS, *this, AI, *NewAI, P.beginOffset(),
+                               P.endOffset(), IsIntegerPromotable, VecTy,
+                               PHIUsers, SelectUsers);
+  bool Promotable = true;
+  for (Slice *S : P.splitSliceTails()) {
+    Promotable &= Rewriter.visit(S);
+    ++NumUses;
+  }
+  for (Slice &S : P) {
+    Promotable &= Rewriter.visit(&S);
+    ++NumUses;
+  }
+
+  NumAllocaPartitionUses += NumUses;
+  MaxUsesPerAllocaPartition.updateMax(NumUses);
+
+  // Now that we've processed all the slices in the new partition, check if any
+  // PHIs or Selects would block promotion.
+  for (PHINode *PHI : PHIUsers)
+    if (!isSafePHIToSpeculate(*PHI)) {
+      Promotable = false;
+      PHIUsers.clear();
+      SelectUsers.clear();
+      break;
+    }
+
+  SmallVector<std::pair<SelectInst *, RewriteableMemOps>, 2>
+      NewSelectsToRewrite;
+  NewSelectsToRewrite.reserve(SelectUsers.size());
+  for (SelectInst *Sel : SelectUsers) {
+    std::optional<RewriteableMemOps> Ops =
+        isSafeSelectToSpeculate(*Sel, PreserveCFG);
+    if (!Ops) {
+      Promotable = false;
+      PHIUsers.clear();
+      SelectUsers.clear();
+      NewSelectsToRewrite.clear();
+      break;
+    }
+    NewSelectsToRewrite.emplace_back(std::make_pair(Sel, *Ops));
+  }
+
+  if (Promotable) {
+    for (Use *U : AS.getDeadUsesIfPromotable()) {
+      auto *OldInst = dyn_cast<Instruction>(U->get());
+      Value::dropDroppableUse(*U);
+      if (OldInst)
+        if (isInstructionTriviallyDead(OldInst))
+          DeadInsts.push_back(OldInst);
+    }
+    if (PHIUsers.empty() && SelectUsers.empty()) {
+      // Promote the alloca.
+      PromotableAllocas.push_back(NewAI);
+    } else {
+      // If we have either PHIs or Selects to speculate, add them to those
+      // worklists and re-queue the new alloca so that we promote in on the
+      // next iteration.
+      for (PHINode *PHIUser : PHIUsers)
+        SpeculatablePHIs.insert(PHIUser);
+      SelectsToRewrite.reserve(SelectsToRewrite.size() +
+                               NewSelectsToRewrite.size());
+      for (auto &&KV : llvm::make_range(
+               std::make_move_iterator(NewSelectsToRewrite.begin()),
+               std::make_move_iterator(NewSelectsToRewrite.end())))
+        SelectsToRewrite.insert(std::move(KV));
+      Worklist.insert(NewAI);
+    }
+  } else {
+    // Drop any post-promotion work items if promotion didn't happen.
+    while (PostPromotionWorklist.size() > PPWOldSize)
+      PostPromotionWorklist.pop_back();
+
+    // We couldn't promote and we didn't create a new partition, nothing
+    // happened.
+    if (NewAI == &AI)
+      return nullptr;
+
+    // If we can't promote the alloca, iterate on it to check for new
+    // refinements exposed by splitting the current alloca. Don't iterate on an
+    // alloca which didn't actually change and didn't get promoted.
+    Worklist.insert(NewAI);
+  }
+
+  return NewAI;
+}
+
+/// Walks the slices of an alloca and form partitions based on them,
+/// rewriting each of their uses.
+bool SROAPass::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
+  if (AS.begin() == AS.end())
+    return false;
+
+  unsigned NumPartitions = 0;
+  bool Changed = false;
+  const DataLayout &DL = AI.getModule()->getDataLayout();
+
+  // First try to pre-split loads and stores.
+  Changed |= presplitLoadsAndStores(AI, AS);
+
+  // Now that we have identified any pre-splitting opportunities,
+  // mark loads and stores unsplittable except for the following case.
+  // We leave a slice splittable if all other slices are disjoint or fully
+  // included in the slice, such as whole-alloca loads and stores.
+  // If we fail to split these during pre-splitting, we want to force them
+  // to be rewritten into a partition.
+  bool IsSorted = true;
+
+  uint64_t AllocaSize =
+      DL.getTypeAllocSize(AI.getAllocatedType()).getFixedValue();
+  const uint64_t MaxBitVectorSize = 1024;
+  if (AllocaSize <= MaxBitVectorSize) {
+    // If a byte boundary is included in any load or store, a slice starting or
+    // ending at the boundary is not splittable.
+    SmallBitVector SplittableOffset(AllocaSize + 1, true);
+    for (Slice &S : AS)
+      for (unsigned O = S.beginOffset() + 1;
+           O < S.endOffset() && O < AllocaSize; O++)
+        SplittableOffset.reset(O);
+
+    for (Slice &S : AS) {
+      if (!S.isSplittable())
+        continue;
+
+      if ((S.beginOffset() > AllocaSize || SplittableOffset[S.beginOffset()]) &&
+          (S.endOffset() > AllocaSize || SplittableOffset[S.endOffset()]))
+        continue;
+
+      if (isa<LoadInst>(S.getUse()->getUser()) ||
+          isa<StoreInst>(S.getUse()->getUser())) {
+        S.makeUnsplittable();
+        IsSorted = false;
+      }
+    }
+  }
+  else {
+    // We only allow whole-alloca splittable loads and stores
+    // for a large alloca to avoid creating too large BitVector.
+    for (Slice &S : AS) {
+      if (!S.isSplittable())
+        continue;
+
+      if (S.beginOffset() == 0 && S.endOffset() >= AllocaSize)
+        continue;
+
+      if (isa<LoadInst>(S.getUse()->getUser()) ||
+          isa<StoreInst>(S.getUse()->getUser())) {
+        S.makeUnsplittable();
+        IsSorted = false;
+      }
+    }
+  }
+
+  if (!IsSorted)
+    llvm::sort(AS);
+
+  /// Describes the allocas introduced by rewritePartition in order to migrate
+  /// the debug info.
+  struct Fragment {
+    AllocaInst *Alloca;
+    uint64_t Offset;
+    uint64_t Size;
+    Fragment(AllocaInst *AI, uint64_t O, uint64_t S)
+      : Alloca(AI), Offset(O), Size(S) {}
+  };
+  SmallVector<Fragment, 4> Fragments;
+
+  // Rewrite each partition.
+  for (auto &P : AS.partitions()) {
+    if (AllocaInst *NewAI = rewritePartition(AI, AS, P)) {
+      Changed = true;
+      if (NewAI != &AI) {
+        uint64_t SizeOfByte = 8;
+        uint64_t AllocaSize =
+            DL.getTypeSizeInBits(NewAI->getAllocatedType()).getFixedValue();
+        // Don't include any padding.
+        uint64_t Size = std::min(AllocaSize, P.size() * SizeOfByte);
+        Fragments.push_back(Fragment(NewAI, P.beginOffset() * SizeOfByte, Size));
+      }
+    }
+    ++NumPartitions;
+  }
+
+  NumAllocaPartitions += NumPartitions;
+  MaxPartitionsPerAlloca.updateMax(NumPartitions);
+
+  // Migrate debug information from the old alloca to the new alloca(s)
+  // and the individual partitions.
+  TinyPtrVector<DbgVariableIntrinsic *> DbgDeclares = FindDbgAddrUses(&AI);
+  for (auto *DbgAssign : at::getAssignmentMarkers(&AI))
+    DbgDeclares.push_back(DbgAssign);
+  for (DbgVariableIntrinsic *DbgDeclare : DbgDeclares) {
+    auto *Expr = DbgDeclare->getExpression();
+    DIBuilder DIB(*AI.getModule(), /*AllowUnresolved*/ false);
+    uint64_t AllocaSize =
+        DL.getTypeSizeInBits(AI.getAllocatedType()).getFixedValue();
+    for (auto Fragment : Fragments) {
+      // Create a fragment expression describing the new partition or reuse AI's
+      // expression if there is only one partition.
+      auto *FragmentExpr = Expr;
+      if (Fragment.Size < AllocaSize || Expr->isFragment()) {
+        // If this alloca is already a scalar replacement of a larger aggregate,
+        // Fragment.Offset describes the offset inside the scalar.
+        auto ExprFragment = Expr->getFragmentInfo();
+        uint64_t Offset = ExprFragment ? ExprFragment->OffsetInBits : 0;
+        uint64_t Start = Offset + Fragment.Offset;
+        uint64_t Size = Fragment.Size;
+        if (ExprFragment) {
+          uint64_t AbsEnd =
+              ExprFragment->OffsetInBits + ExprFragment->SizeInBits;
+          if (Start >= AbsEnd) {
+            // No need to describe a SROAed padding.
+            continue;
+          }
+          Size = std::min(Size, AbsEnd - Start);
+        }
+        // The new, smaller fragment is stenciled out from the old fragment.
+        if (auto OrigFragment = FragmentExpr->getFragmentInfo()) {
+          assert(Start >= OrigFragment->OffsetInBits &&
+                 "new fragment is outside of original fragment");
+          Start -= OrigFragment->OffsetInBits;
+        }
+
+        // The alloca may be larger than the variable.
+        auto VarSize = DbgDeclare->getVariable()->getSizeInBits();
+        if (VarSize) {
+          if (Size > *VarSize)
+            Size = *VarSize;
+          if (Size == 0 || Start + Size > *VarSize)
+            continue;
+        }
+
+        // Avoid creating a fragment expression that covers the entire variable.
+        if (!VarSize || *VarSize != Size) {
+          if (auto E =
+                  DIExpression::createFragmentExpression(Expr, Start, Size))
+            FragmentExpr = *E;
+          else
+            continue;
+        }
+      }
+
+      // Remove any existing intrinsics on the new alloca describing
+      // the variable fragment.
+      for (DbgVariableIntrinsic *OldDII : FindDbgAddrUses(Fragment.Alloca)) {
+        auto SameVariableFragment = [](const DbgVariableIntrinsic *LHS,
+                                       const DbgVariableIntrinsic *RHS) {
+          return LHS->getVariable() == RHS->getVariable() &&
+                 LHS->getDebugLoc()->getInlinedAt() ==
+                     RHS->getDebugLoc()->getInlinedAt();
+        };
+        if (SameVariableFragment(OldDII, DbgDeclare))
+          OldDII->eraseFromParent();
+      }
+
+      if (auto *DbgAssign = dyn_cast<DbgAssignIntrinsic>(DbgDeclare)) {
+        if (!Fragment.Alloca->hasMetadata(LLVMContext::MD_DIAssignID)) {
+          Fragment.Alloca->setMetadata(
+              LLVMContext::MD_DIAssignID,
+              DIAssignID::getDistinct(AI.getContext()));
+        }
+        auto *NewAssign = DIB.insertDbgAssign(
+            Fragment.Alloca, DbgAssign->getValue(), DbgAssign->getVariable(),
+            FragmentExpr, Fragment.Alloca, DbgAssign->getAddressExpression(),
+            DbgAssign->getDebugLoc());
+        NewAssign->setDebugLoc(DbgAssign->getDebugLoc());
+        LLVM_DEBUG(dbgs() << "Created new assign intrinsic: " << *NewAssign
+                          << "\n");
+      } else {
+        DIB.insertDeclare(Fragment.Alloca, DbgDeclare->getVariable(),
+                          FragmentExpr, DbgDeclare->getDebugLoc(), &AI);
+      }
+    }
+  }
+  return Changed;
+}
+
+/// Clobber a use with poison, deleting the used value if it becomes dead.
+void SROAPass::clobberUse(Use &U) {
+  Value *OldV = U;
+  // Replace the use with an poison value.
+  U = PoisonValue::get(OldV->getType());
+
+  // Check for this making an instruction dead. We have to garbage collect
+  // all the dead instructions to ensure the uses of any alloca end up being
+  // minimal.
+  if (Instruction *OldI = dyn_cast<Instruction>(OldV))
+    if (isInstructionTriviallyDead(OldI)) {
+      DeadInsts.push_back(OldI);
+    }
+}
+
+/// Analyze an alloca for SROA.
+///
+/// This analyzes the alloca to ensure we can reason about it, builds
+/// the slices of the alloca, and then hands it off to be split and
+/// rewritten as needed.
+std::pair<bool /*Changed*/, bool /*CFGChanged*/>
+SROAPass::runOnAlloca(AllocaInst &AI) {
+  bool Changed = false;
+  bool CFGChanged = false;
+
+  LLVM_DEBUG(dbgs() << "SROA alloca: " << AI << "\n");
+  ++NumAllocasAnalyzed;
+
+  // Special case dead allocas, as they're trivial.
+  if (AI.use_empty()) {
+    AI.eraseFromParent();
+    Changed = true;
+    return {Changed, CFGChanged};
+  }
+  const DataLayout &DL = AI.getModule()->getDataLayout();
+
+  // Skip alloca forms that this analysis can't handle.
+  auto *AT = AI.getAllocatedType();
+  if (AI.isArrayAllocation() || !AT->isSized() || isa<ScalableVectorType>(AT) ||
+      DL.getTypeAllocSize(AT).getFixedValue() == 0)
+    return {Changed, CFGChanged};
+
+  // First, split any FCA loads and stores touching this alloca to promote
+  // better splitting and promotion opportunities.
+  IRBuilderTy IRB(&AI);
+  AggLoadStoreRewriter AggRewriter(DL, IRB);
+  Changed |= AggRewriter.rewrite(AI);
+
+  // Build the slices using a recursive instruction-visiting builder.
+  AllocaSlices AS(DL, AI);
+  LLVM_DEBUG(AS.print(dbgs()));
+  if (AS.isEscaped())
+    return {Changed, CFGChanged};
+
+  // Delete all the dead users of this alloca before splitting and rewriting it.
+  for (Instruction *DeadUser : AS.getDeadUsers()) {
+    // Free up everything used by this instruction.
+    for (Use &DeadOp : DeadUser->operands())
+      clobberUse(DeadOp);
+
+    // Now replace the uses of this instruction.
+    DeadUser->replaceAllUsesWith(PoisonValue::get(DeadUser->getType()));
+
+    // And mark it for deletion.
+    DeadInsts.push_back(DeadUser);
+    Changed = true;
+  }
+  for (Use *DeadOp : AS.getDeadOperands()) {
+    clobberUse(*DeadOp);
+    Changed = true;
+  }
+
+  // No slices to split. Leave the dead alloca for a later pass to clean up.
+  if (AS.begin() == AS.end())
+    return {Changed, CFGChanged};
+
+  Changed |= splitAlloca(AI, AS);
+
+  LLVM_DEBUG(dbgs() << "  Speculating PHIs\n");
+  while (!SpeculatablePHIs.empty())
+    speculatePHINodeLoads(IRB, *SpeculatablePHIs.pop_back_val());
+
+  LLVM_DEBUG(dbgs() << "  Rewriting Selects\n");
+  auto RemainingSelectsToRewrite = SelectsToRewrite.takeVector();
+  while (!RemainingSelectsToRewrite.empty()) {
+    const auto [K, V] = RemainingSelectsToRewrite.pop_back_val();
+    CFGChanged |=
+        rewriteSelectInstMemOps(*K, V, IRB, PreserveCFG ? nullptr : DTU);
+  }
+
+  return {Changed, CFGChanged};
+}
+
+/// Delete the dead instructions accumulated in this run.
+///
+/// Recursively deletes the dead instructions we've accumulated. This is done
+/// at the very end to maximize locality of the recursive delete and to
+/// minimize the problems of invalidated instruction pointers as such pointers
+/// are used heavily in the intermediate stages of the algorithm.
+///
+/// We also record the alloca instructions deleted here so that they aren't
+/// subsequently handed to mem2reg to promote.
+bool SROAPass::deleteDeadInstructions(
+    SmallPtrSetImpl<AllocaInst *> &DeletedAllocas) {
+  bool Changed = false;
+  while (!DeadInsts.empty()) {
+    Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
+    if (!I)
+      continue;
+    LLVM_DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
+
+    // If the instruction is an alloca, find the possible dbg.declare connected
+    // to it, and remove it too. We must do this before calling RAUW or we will
+    // not be able to find it.
+    if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
+      DeletedAllocas.insert(AI);
+      for (DbgVariableIntrinsic *OldDII : FindDbgAddrUses(AI))
+        OldDII->eraseFromParent();
+    }
+
+    at::deleteAssignmentMarkers(I);
+    I->replaceAllUsesWith(UndefValue::get(I->getType()));
+
+    for (Use &Operand : I->operands())
+      if (Instruction *U = dyn_cast<Instruction>(Operand)) {
+        // Zero out the operand and see if it becomes trivially dead.
+        Operand = nullptr;
+        if (isInstructionTriviallyDead(U))
+          DeadInsts.push_back(U);
+      }
+
+    ++NumDeleted;
+    I->eraseFromParent();
+    Changed = true;
+  }
+  return Changed;
+}
+
+/// Promote the allocas, using the best available technique.
+///
+/// This attempts to promote whatever allocas have been identified as viable in
+/// the PromotableAllocas list. If that list is empty, there is nothing to do.
+/// This function returns whether any promotion occurred.
+bool SROAPass::promoteAllocas(Function &F) {
+  if (PromotableAllocas.empty())
+    return false;
+
+  NumPromoted += PromotableAllocas.size();
+
+  LLVM_DEBUG(dbgs() << "Promoting allocas with mem2reg...\n");
+  PromoteMemToReg(PromotableAllocas, DTU->getDomTree(), AC);
+  PromotableAllocas.clear();
+  return true;
+}
+
+PreservedAnalyses SROAPass::runImpl(Function &F, DomTreeUpdater &RunDTU,
+                                    AssumptionCache &RunAC) {
+  LLVM_DEBUG(dbgs() << "SROA function: " << F.getName() << "\n");
+  C = &F.getContext();
+  DTU = &RunDTU;
+  AC = &RunAC;
+
+  BasicBlock &EntryBB = F.getEntryBlock();
+  for (BasicBlock::iterator I = EntryBB.begin(), E = std::prev(EntryBB.end());
+       I != E; ++I) {
+    if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
+      if (isa<ScalableVectorType>(AI->getAllocatedType())) {
+        if (isAllocaPromotable(AI))
+          PromotableAllocas.push_back(AI);
+      } else {
+        Worklist.insert(AI);
+      }
+    }
+  }
+
+  bool Changed = false;
+  bool CFGChanged = false;
+  // A set of deleted alloca instruction pointers which should be removed from
+  // the list of promotable allocas.
+  SmallPtrSet<AllocaInst *, 4> DeletedAllocas;
+
+  do {
+    while (!Worklist.empty()) {
+      auto [IterationChanged, IterationCFGChanged] =
+          runOnAlloca(*Worklist.pop_back_val());
+      Changed |= IterationChanged;
+      CFGChanged |= IterationCFGChanged;
+
+      Changed |= deleteDeadInstructions(DeletedAllocas);
+
+      // Remove the deleted allocas from various lists so that we don't try to
+      // continue processing them.
+      if (!DeletedAllocas.empty()) {
+        auto IsInSet = [&](AllocaInst *AI) { return DeletedAllocas.count(AI); };
+        Worklist.remove_if(IsInSet);
+        PostPromotionWorklist.remove_if(IsInSet);
+        llvm::erase_if(PromotableAllocas, IsInSet);
+        DeletedAllocas.clear();
+      }
+    }
+
+    Changed |= promoteAllocas(F);
+
+    Worklist = PostPromotionWorklist;
+    PostPromotionWorklist.clear();
+  } while (!Worklist.empty());
+
+  assert((!CFGChanged || Changed) && "Can not only modify the CFG.");
+  assert((!CFGChanged || !PreserveCFG) &&
+         "Should not have modified the CFG when told to preserve it.");
+
+  if (!Changed)
+    return PreservedAnalyses::all();
+
+  PreservedAnalyses PA;
+  if (!CFGChanged)
+    PA.preserveSet<CFGAnalyses>();
+  PA.preserve<DominatorTreeAnalysis>();
+  return PA;
+}
+
+PreservedAnalyses SROAPass::runImpl(Function &F, DominatorTree &RunDT,
+                                    AssumptionCache &RunAC) {
+  DomTreeUpdater DTU(RunDT, DomTreeUpdater::UpdateStrategy::Lazy);
+  return runImpl(F, DTU, RunAC);
+}
+
+PreservedAnalyses SROAPass::run(Function &F, FunctionAnalysisManager &AM) {
+  return runImpl(F, AM.getResult<DominatorTreeAnalysis>(F),
+                 AM.getResult<AssumptionAnalysis>(F));
+}
+
+void SROAPass::printPipeline(
+    raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
+  static_cast<PassInfoMixin<SROAPass> *>(this)->printPipeline(
+      OS, MapClassName2PassName);
+  OS << (PreserveCFG ? "<preserve-cfg>" : "<modify-cfg>");
+}
+
+SROAPass::SROAPass(SROAOptions PreserveCFG_)
+    : PreserveCFG(PreserveCFG_ == SROAOptions::PreserveCFG) {}
+
+/// A legacy pass for the legacy pass manager that wraps the \c SROA pass.
+///
+/// This is in the llvm namespace purely to allow it to be a friend of the \c
+/// SROA pass.
+class llvm::sroa::SROALegacyPass : public FunctionPass {
+  /// The SROA implementation.
+  SROAPass Impl;
+
+public:
+  static char ID;
+
+  SROALegacyPass(SROAOptions PreserveCFG = SROAOptions::PreserveCFG)
+      : FunctionPass(ID), Impl(PreserveCFG) {
+    initializeSROALegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override {
+    if (skipFunction(F))
+      return false;
+
+    auto PA = Impl.runImpl(
+        F, getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
+        getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F));
+    return !PA.areAllPreserved();
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<AssumptionCacheTracker>();
+    AU.addRequired<DominatorTreeWrapperPass>();
+    AU.addPreserved<GlobalsAAWrapperPass>();
+    AU.addPreserved<DominatorTreeWrapperPass>();
+  }
+
+  StringRef getPassName() const override { return "SROA"; }
+};
+
+char SROALegacyPass::ID = 0;
+
+FunctionPass *llvm::createSROAPass(bool PreserveCFG) {
+  return new SROALegacyPass(PreserveCFG ? SROAOptions::PreserveCFG
+                                        : SROAOptions::ModifyCFG);
+}
+
+INITIALIZE_PASS_BEGIN(SROALegacyPass, "sroa",
+                      "Scalar Replacement Of Aggregates", false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_END(SROALegacyPass, "sroa", "Scalar Replacement Of Aggregates",
+                    false, false)